Fix deprecation warnings with recent compilers and CMake

[schwicke]

Some things to be fixed in recent versions of cmake:

CMake Deprecation Warning at CMakeLists.txt:1 (CMAKE_MINIMUM_REQUIRED):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

and clang:

src/libphigs/css/css_el.c:85:52: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:98:3: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:101:7: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:109:7: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:362:6: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
5 warnings generated.
src/libphigs/css/css_inq.c:121:6: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_inq.c:159:3: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
2 warnings generated.
src/libphigs/css/css_str.c:149:9: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_str.c:852:6: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
2 warnings generated.
src/libphigs/ut/ut_htab.c:154:19: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
1 warning generated.
src/libphigs/phg/phg.c:497:10: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
1 warning generated.
src/libphigs/ws/ws_inp.c:1379:43: warning: implicit conversion from enumeration type 'Pin_class' to different enumeration type 'Phg_args_idev_class' [-Wenum-conversion]
1 warning generated.
src/libphigs/ws/wstx_ini.c:324:29: warning: implicit conversion from enumeration type 'Wst_loc_type' to different enumeration type 'Wst_stroke_type' [-Wenum-conversion]
src/libphigs/ws/wstx_ini.c:333:27: warning: implicit conversion from enumeration type 'Wst_loc_type' to different enumeration type 'Wst_pick_type' [-Wenum-conversion]
2 warnings generated.
src/libphigs/errors/err.c:45:4: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/errors/err.c:96:7: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
2 warnings generated.
src/libphigs/c_binding/cb_lite.c:41:6: warning: a function definition without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
1 warning generated.
src/libphigs/css/css_el.c:85:52: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:98:3: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:101:7: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:109:7: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_el.c:362:6: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
5 warnings generated.
src/libphigs/css/css_inq.c:121:6: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_inq.c:159:3: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
2 warnings generated.
src/libphigs/css/css_str.c:149:9: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/css/css_str.c:852:6: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
2 warnings generated.
src/libphigs/ut/ut_htab.c:154:19: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
1 warning generated.
src/libphigs/phg/phg.c:497:10: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
1 warning generated.
src/libphigs/ws/ws_inp.c:1379:43: warning: implicit conversion from enumeration type 'Pin_class' to different enumeration type 'Phg_args_idev_class' [-Wenum-conversion]
1 warning generated.
src/libphigs/ws/wstx_ini.c:324:29: warning: implicit conversion from enumeration type 'Wst_loc_type' to different enumeration type 'Wst_stroke_type' [-Wenum-conversion]
src/libphigs/ws/wstx_ini.c:333:27: warning: implicit conversion from enumeration type 'Wst_loc_type' to different enumeration type 'Wst_pick_type' [-Wenum-conversion]
2 warnings generated.
src/libphigs/errors/err.c:45:4: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
src/libphigs/errors/err.c:96:7: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Wdeprecated-non-prototype]
2 warnings generated.