maintainer-feedback requested: [Bug 268301] x11-toolkits/pangox-compat: fix build with clang 15

Bugzilla Automation <bugzilla@FreeBSD.org> has asked freebsd-gnome (Nobody)
<gnome@FreeBSD.org> for maintainer-feedback:
Bug 268301: x11-toolkits/pangox-compat: fix build with clang 15
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=268301



--- Description ---
During an exp-run for llvm 15 (see bug 265425), it turned out that
x11-toolkits/pangox-compat failed to build with clang 15:

  pangox.c:983:15: error: incompatible integer to pointer conversion assigning
to 'PangoFontMetrics *' (aka 'struct _PangoFontMetrics *') from 'int'
[-Wint-conversion]
	metrics = pango_font_metrics_new ();
		^ ~~~~~~~~~~~~~~~~~~~~~~~~~
  pangox-fontmap.c:944:9: error: incompatible integer to pointer conversion
initializing 'char *' with an expression of type 'int' [-Wint-conversion]
    char *files_str = pango_config_key_get ("PangoX/AliasFiles");
	  ^	      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is because pangox-compat uses two private functions from the main pango
library, which are not declared in the public pango headers.

Fix the errors by adding the two private functions in pango-impl-utils.h,
copying the declarations from pango-font-private.h and pango-utils-private.h.