Add 'use_gnu_ext' option

Controls the USE_GNU_EXTENSIONS define in compat.h

meson.build

@@ -271,6 +271,8 @@ else
     config.set('TAISEI_BUILDCONF_HAVE_MAX_ALIGN_T', malloc_alignment > 0)
 endif
 
+config.set('TAISEI_BUILDCONF_USE_GNU_EXTENSIONS', get_option('use_gnu_ext'))
+
 prefer_relpath_systems = [
     'windows',
 ]

meson_options.txt

@@ -190,3 +190,10 @@ option(
     value : false,
     description : 'Build shaderc and spirv-cross CLI tools from subprojects even if system versions exist'
 )
+
+option(
+    'use_gnu_ext',
+    type : 'boolean',
+    value : true,
+    description : 'Allow use of some GNU C extensions (if supported by compiler)'
+)

src/util/compat.h

@@ -81,7 +81,9 @@
 	#define DIAGNOSTIC_GCC(x)
 	#define DIAGNOSTIC_CLANG(x)
 #else
-	#define USE_GNU_EXTENSIONS
+	#ifdef TAISEI_BUILDCONF_USE_GNU_EXTENSIONS
+		#define USE_GNU_EXTENSIONS
+	#endif
 	#define UNREACHABLE __builtin_unreachable()
 
 	#define DIAGNOSTIC(x) PRAGMA(GCC diagnostic x)