Add strcasecmp() and strncasecmp()

strncasecmp() is present as strnicmp() but disabled. Make it available
and define strcasecmp() also. There is a only a small performance penalty
to having strcasecmp() call strncasecmp(), so do this instead of a
standalone function, to save code space.

Update the prototype in arch-specific headers as needed to avoid warnings.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/linux/string.h b/include/linux/string.h
index 9a8cbc2..de83355 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -38,8 +38,11 @@
 #ifndef __HAVE_ARCH_STRNCMP
 extern int strncmp(const char *,const char *,__kernel_size_t);
 #endif
-#if 0 /* not used - was: #ifndef __HAVE_ARCH_STRNICMP */
-extern int strnicmp(const char *, const char *, __kernel_size_t);
+#ifndef __HAVE_ARCH_STRCASECMP
+int strcasecmp(const char *s1, const char *s2);
+#endif
+#ifndef __HAVE_ARCH_STRNCASECMP
+extern int strncasecmp(const char *s1, const char *s2, __kernel_size_t len);
 #endif
 #ifndef __HAVE_ARCH_STRCHR
 extern char * strchr(const char *,int);