Import strcasestr() from musl and remove -D_GNU_SOURCE

Makefile

@@ -48,6 +48,7 @@ LIBUTILSRC =\
 	libutil/sha1.c\
 	libutil/sha256.c\
 	libutil/sha512.c\
+	libutil/strcasestr.c\
 	libutil/strlcat.c\
 	libutil/strlcpy.c
 

config.mk

@@ -10,6 +10,6 @@ LD = $(CC)
 AR = ar
 RANLIB = ranlib
 
-CPPFLAGS = -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_GNU_SOURCE
+CPPFLAGS = -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_XOPEN_SOURCE=700
 CFLAGS   = -std=c99 -Wall -pedantic
 LDFLAGS  = -s

grep.c

@@ -3,7 +3,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <strings.h>
 #include <unistd.h>
 
 #include "queue.h"

libutil/strcasestr.c

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2005-2014 Rich Felker, et al.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+#include <string.h>
+
+#include "../util.h"
+
+char *
+strcasestr(const char *h, const char *n)
+{
+        size_t l = strlen(n);
+        for (; *h; h++) if (!strncasecmp(h, n, l)) return (char *)h;
+        return 0;
+}

util.h

@@ -33,6 +33,9 @@ void weprintf(const char *, ...);
 double estrtod(const char *);
 long estrtol(const char *, int);
 
+#undef strcasestr
+char *strcasestr(const char *, const char *);
+
 #undef strlcat
 size_t strlcat(char *, const char *, size_t);
 #undef strlcpy