enh(c) add C23 keywords and types (#3836)

CHANGES.md

@@ -6,6 +6,7 @@ CAVEATS / POTENTIALLY BREAKING CHANGES
 
 Core Grammars:
 
+- enh(c) added more C23 keywords and preprcoessor directives [Eisenwave][]
 - enh(js/ts) support namespaced tagged template strings [Aral Balkan][]
 - enh(perl) fix false-positive variable match at end of string [Josh Goebel][]
 - fix(cpp) not all kinds of number literals are highlighted correctly [Lê Duy Quang][]
@@ -55,6 +56,7 @@ Themes:
 
 - Added `1c-light` theme a like in the IDE 1C:Enterprise 8 (for 1c) [Vitaly Barilko][]
 
+[Eisenwave]: https://github.com/Eisenwave 
 [Aral Balkan]: https://github.com/aral
 [Lê Duy Quang]: https://github.com/leduyquang753
 [Mohamed Ali]: https://github.com/MohamedAli00949
@@ -134,7 +136,6 @@ Core Grammars:
 - fix(css) added '_'  css variable detection [Md Saad Akhtar][]
 - enh(groovy) add `record` and `var` as keywords [Guillaume Laforge][]
 
-
 Developer Tool:
 
 - (chore) Update dev tool to use the new `highlight` API. [Shah Shabbir Ahmmed][]

src/languages/c.js

@@ -70,7 +70,7 @@ export default function(hljs) {
     end: /$/,
     keywords: { keyword:
         'if else elif endif define undef warning error line '
-        + 'pragma _Pragma ifdef ifndef include' },
+        + 'pragma _Pragma ifdef ifndef elifdef elifndef include' },
     contains: [
       {
         begin: /\\\n/,
@@ -148,14 +148,26 @@ export default function(hljs) {
     "char",
     "void",
     "_Bool",
+    "_BitInt",
     "_Complex",
     "_Imaginary",
     "_Decimal32",
     "_Decimal64",
+    "_Decimal96",
     "_Decimal128",
+    "_Decimal64x",
+    "_Decimal128x",
+    "_Float16",
+    "_Float32",
+    "_Float64",
+    "_Float128",
+    "_Float32x",
+    "_Float64x",
+    "_Float128x",
     // modifiers
     "const",
     "static",
+    "constexpr",
     // aliases
     "complex",
     "bool",