[C] Add support for C23 _BitInt type

This is implemented like typeof() because it can only be used with
()s to indicate how many bits the resulting integer type will have.

While I was at it, I also added support for the new suffixes for
_BitInt integer constants.

C++/C.sublime-syntax

@@ -33,7 +33,7 @@ variables:
   hex_suffix: '[g-zG-Z_][[:alnum:]_]*'
   double_suffix: '[fFlL]'
   float_suffix: '[fF]'
-  integer_suffix: '[lL]{1,2}[uU]?|[uU][lL]{0,2}'
+  integer_suffix: 'u?wb|[lL]{1,2}[uU]?|[uU][lL]{0,2}'
 
   identifier: \b[[:alpha:]_][[:alnum:]_]*\b # upper and lowercase
   macro_identifier: \b[[:upper:]_][[:upper:][:digit:]_]{2,}\b # only uppercase, at least 3 chars
@@ -51,7 +51,7 @@ variables:
   type_qualifier: 'const|volatile|_Atomic'
   compiler_directive: 'inline|restrict|__restrict__|__restrict|_Noreturn|noreturn'
   modifiers: '{{storage_classes}}|{{type_qualifier}}|{{compiler_directive}}'
-  non_func_keywords: 'if|for|switch|while|decltype|typeof|typeof_unqual|_Atomic|sizeof|alignof|_Alignof|static_assert|_Static_assert|__declspec|__attribute__'
+  non_func_keywords: 'if|for|switch|while|decltype|typeof|typeof_unqual|_Atomic|_BitInt|sizeof|alignof|_Alignof|static_assert|_Static_assert|__declspec|__attribute__'
 
 contexts:
   main:
@@ -260,7 +260,7 @@ contexts:
     - include: types-parens
 
   types-parens:
-    - match: '\b(typeof|__typeof|__typeof__|typeof_unqual|_Atomic)\b\s*(\()'
+    - match: '\b(typeof|__typeof|__typeof__|typeof_unqual|_Atomic|_BitInt)\b\s*(\()'
       captures:
         1: keyword.declaration.type.c
         2: meta.group.c punctuation.section.group.begin.c

C++/syntax_test_c.c

@@ -201,6 +201,14 @@ struct foo {
 int i;
 /* <- storage.type */
 
+signed _BitInt(4) bi1 = 1wb;
+/*     ^ keyword.declaration.type */
+/*                       ^ constant.numeric.suffix */
+
+unsigned _BitInt(4) bi2 = 1uwb;
+/*       ^ keyword.declaration.type */
+/*                         ^ constant.numeric.suffix */
+
 _Atomic int ai1;
 /* <- storage.modifier */