[NFC][llvm][support] rename INFINITY in regcomp (llvm#101758)

since C23 this macro is defined by float.h, which clang implements in
it's float.h since llvm#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.

(cherry picked from commit 899f648)

llvm/lib/Support/regcomp.c

@@ -278,7 +278,7 @@ 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 */
@@ -582,7 +582,7 @@ 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);
@@ -753,7 +753,7 @@ 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);
@@ -1115,7 +1115,7 @@ 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 */