regex: make ExperimentalRegexBridging.h C friendly

`bool` is not a valid type in C.  However, C99 does provide `stdboo.h`
to help bridge that type.

Author: compnerd

include/swift/Parse/ExperimentalRegexBridging.h

@@ -1,6 +1,8 @@
 #ifndef EXPERIMENTAL_REGEX_BRIDGING
 #define EXPERIMENTAL_REGEX_BRIDGING
 
+#include <stdbool.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -19,9 +21,9 @@ extern "C" {
 /// Returns: A bool indicating whether lexing was completely erroneous, and
 ///          cannot be recovered from, or false if there either was no error,
 ///          or there was a recoverable error.
-typedef bool(* RegexLiteralLexingFn)(/*CurPtrPtr*/ const char **,
-                                     /*BufferEnd*/ const char *,
-                                     /*ErrorOut*/ const char **);
+typedef bool (* RegexLiteralLexingFn)(/*CurPtrPtr*/ const char **,
+                                      /*BufferEnd*/ const char *,
+                                      /*ErrorOut*/ const char **);
 void Parser_registerRegexLiteralLexingFn(RegexLiteralLexingFn fn);
 
 /// Parse a regex literal string. Takes the following arguments: