[Linux] Helper methods for pkg-config

- Fixes linking on GCC by putting libs in link group

premake5.lua

@@ -99,8 +99,8 @@ filter("platforms:Linux")
   toolset("clang")
   buildoptions({
     -- "-mlzcnt",  -- (don't) Assume lzcnt is supported.
-    ({os.outputof("pkg-config --cflags gtk+-x11-3.0")})[1],
   })
+  pkg_config.all("gtk+-x11-3.0")
   links({
     "stdc++fs",
     "dl",
@@ -108,9 +108,6 @@ filter("platforms:Linux")
     "pthread",
     "rt",
   })
-  linkoptions({
-    ({os.outputof("pkg-config --libs gtk+-3.0")})[1],
-  })
 
 filter({"platforms:Linux", "kind:*App"})
   linkgroups("On")