regex: convert #if to #ifdef

Avoid gcc warnings about #if statements with defines that aren't defined.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

libc/misc/regex/regex_internal.c

@@ -602,7 +602,7 @@ re_string_reconstruct (re_string_t *pstr, int idx, int eflags)
 		     pstr->valid_len - offset);
 	  pstr->valid_len -= offset;
 	  pstr->valid_raw_len -= offset;
-#if DEBUG
+#ifdef DEBUG
 	  assert (pstr->valid_len > 0);
 #endif
 	}

libc/misc/regex/regex_internal.h

@@ -361,7 +361,7 @@ static unsigned int re_string_context_at (const re_string_t *input, int idx,
 #include <alloca.h>
 
 #if 1
-# if HAVE_ALLOCA
+# ifdef HAVE_ALLOCA
 /* The OS usually guarantees only one guard page at the bottom of the stack,
    and a page size can be as small as 4096 bytes.  So we cannot safely
    allocate anything larger than 4096 bytes.  Also care for the possibility