meson: combine checks for linker --gc-sections support

We first do an incomplete check for whether the linker supports
--gc-sections, then potentially add C and C++ arguments assuming that it
works, then later do a complete check to see if it actually works and
use --gc-sections. This means we can end up putting functions and data
in separate sections when we can't gc them.

Combine the checks, do less work, and be more accurate.

fixes: f51ce21e4e
       ("meson: Drop adding -Wl,--gc-sections to project c/cpp arguments.")

Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21083>

meson.build

@@ -965,6 +965,7 @@ endif
 c_msvc_compat_args = []
 no_override_init_args = []
 cpp_msvc_compat_args = []
+ld_args_gc_sections = []
 if cc.get_argument_syntax() == 'msvc'
   _trial = [
     '/wd4018',  # signed/unsigned mismatch
@@ -1044,7 +1045,9 @@ else
   # own sections and GC the sections after linking.  This lets drivers
   # drop shared code unused by that specific driver (particularly
   # relevant for Vulkan drivers).
-  if cc.has_link_argument('-Wl,--gc-sections')
+  if cc.links('static char unused() { return 5; } int main() { return 0; }',
+              args : '-Wl,--gc-sections', name : 'gc-sections')
+    ld_args_gc_sections += '-Wl,--gc-sections'
     _trial_c += ['-ffunction-sections', '-fdata-sections']
     _trial_cpp += ['-ffunction-sections', '-fdata-sections']
   endif
@@ -1380,11 +1383,6 @@ ld_args_bsymbolic = []
 if cc.links('int main() { return 0; }', args : '-Wl,-Bsymbolic', name : 'Bsymbolic')
   ld_args_bsymbolic += '-Wl,-Bsymbolic'
 endif
-ld_args_gc_sections = []
-if cc.links('static char unused() { return 5; } int main() { return 0; }',
-            args : '-Wl,--gc-sections', name : 'gc-sections')
-  ld_args_gc_sections += '-Wl,--gc-sections'
-endif
 with_ld_version_script = false
 if cc.links('int main() { return 0; }',
             args : '-Wl,--version-script=@0@'.format(