Fix -Wundef warnings by using #ifdef instead of #if

This also brings back the check for __func__ that was deleted in commit
9b41a09

configure.ac

@@ -196,6 +196,7 @@ AC_CHECK_FUNCS([dup2 memset regcomp strcasecmp strchr strdup strtol], [],
 # reallocarr - NetBSD function. Use reallocarray if not available.
 # reallocarray - OpenBSD function. We have replacement if not available.
 AC_CHECK_FUNCS([pow setlocale reallocarr reallocarray])
+AC_CHECK_DECLS(__func__)
 
 AS_IF([test "$cross_compiling" = yes],
   [AC_CONFIG_FILES([src/config_for_build.h])])

src/flexdef.h

@@ -889,7 +889,7 @@ extern void flexerror(const char *);
 extern void flexfatal(const char *);
 
 /* Report a fatal error with a pinpoint, and terminate */
-#if HAVE_DECL___FUNC__
+#ifdef HAVE_DECL___FUNC__
 #define flex_die(msg) \
     do{ \
         fprintf (stderr,\

src/misc.c

@@ -64,12 +64,12 @@ void add_action (const char *new_text)
 void   *allocate_array (int size, size_t element_size)
 {
 	void *new_array;
-#if HAVE_REALLOCARR
+#ifdef HAVE_REALLOCARR
 	new_array = NULL;
 	if (reallocarr(&new_array, (size_t) size, element_size))
 		flexfatal (_("memory allocation failed in allocate_array()"));
 #else
-# if HAVE_REALLOCARRAY
+# ifdef HAVE_REALLOCARRAY
 	new_array = reallocarray(NULL, (size_t) size, element_size);
 # else
 	/* Do manual overflow detection */
@@ -580,12 +580,12 @@ char   *readable_form (int c)
 void   *reallocate_array (void *array, int size, size_t element_size)
 {
 	void *new_array;
-#if HAVE_REALLOCARR
+#ifdef HAVE_REALLOCARR
 	new_array = array;
 	if (reallocarr(&new_array, (size_t) size, element_size))
 		flexfatal (_("attempt to increase array size failed"));
 #else
-# if HAVE_REALLOCARRAY
+# ifdef HAVE_REALLOCARRAY
 	new_array = reallocarray(array, (size_t) size, element_size);
 # else
 	/* Do manual overflow detection */