Set default LanguageStandard for C projects to gnu23.

Author: alexrp

src/sdk/build/Vezel.Zig.Sdk.Defaults.targets

@@ -23,7 +23,7 @@
     </PropertyGroup>
 
     <PropertyGroup Condition="'$(LanguageStandard)' == ''">
-        <LanguageStandard Condition="'$(Language)' == 'C'">gnu2x</LanguageStandard>
+        <LanguageStandard Condition="'$(Language)' == 'C'">gnu23</LanguageStandard>
         <LanguageStandard Condition="'$(Language)' == 'Cxx'">gnu++2c</LanguageStandard>
         <LanguageStandard Condition="'$(Language)' == 'Zig'">zig</LanguageStandard>
     </PropertyGroup>