Rename INFINITY in regcomp

Summary:
LLVM 19 started to introduce defining some of the [math macros](https://github.com/llvm/llvm-project/blob/eb2929d323c0c44f2037cf8a345ca6984ec228eb/clang/lib/Headers/float.h#L170-L179) in the compiler leading to warnings-turned-errors macro redefinitions.

 ---
> since C23 this macro is defined by float.h, which clang implements in
it's float.h since #96659 landed.
> However, regcomp.c in LLVMSupport happened to define it's own macro with
that name, leading to problems when bootstrapping. This change renames
the offending macro.

Original commit: llvm/llvm-project@899f648

Reviewed By: smeenai

Differential Revision: D62278490

fbshipit-source-id: 2ec4f025876a0294bb749b4224baf52de9c28158

external/llvh/lib/Support/regcomp.c

@@ -287,7 +287,7 @@ static char nuls[10];		/* place to point scanner in event of error */
 #else
 #define	DUPMAX	255
 #endif
-#define	INFINITY	(DUPMAX + 1)
+#define REGINFINITY (DUPMAX + 1)
 
 #ifndef NDEBUG
 static int never = 0;		/* for use in asserts; shuts lint up */
@@ -591,7 +591,7 @@ p_ere_exp(struct parse *p)
 				count2 = p_count(p);
 				REQUIRE(count <= count2, REG_BADBR);
 			} else		/* single number with comma */
-				count2 = INFINITY;
+				count2 = REGINFINITY;
 		} else		/* just a single number */
 			count2 = count;
 		repeat(p, pos, count, count2);
@@ -762,7 +762,7 @@ p_simp_re(struct parse *p,
 				count2 = p_count(p);
 				REQUIRE(count <= count2, REG_BADBR);
 			} else		/* single number with comma */
-				count2 = INFINITY;
+				count2 = REGINFINITY;
 		} else		/* just a single number */
 			count2 = count;
 		repeat(p, pos, count, count2);
@@ -1126,7 +1126,7 @@ repeat(struct parse *p,
 #	define	N	2
 #	define	INF	3
 #	define	REP(f, t)	((f)*8 + (t))
-#	define	MAP(n)	(((n) <= 1) ? (n) : ((n) == INFINITY) ? INF : N)
+#	define	MAP(n)	(((n) <= 1) ? (n) : ((n) == REGINFINITY) ? INF : N)
 	sopno copy;
 
 	if (p->error != 0)	/* head off possible runaway recursion */