mtools: Fix build with clang

Identify with __clang__ to undefine UNUSED

(From OE-Core rev: fcede6dd3e44d9f7761d058db76dfaf103b75c6a)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/mtools/mtools/clang_UNUSED.patch

@@ -0,0 +1,17 @@
+Undefine UNUSED macros with clang
+
+Upstream-Status: Pending
+Signed-off-by: Khem Raj <raj.khem@gmail.com>
+Index: mtools-4.0.18/sysincludes.h
+===================================================================
+--- mtools-4.0.18.orig/sysincludes.h
++++ mtools-4.0.18/sysincludes.h
+@@ -101,7 +101,7 @@ typedef void *caddr_t;
+ #if defined __GNUC__ && defined __STDC__
+ /* gcc -traditional doesn't have PACKED, UNUSED and NORETURN */
+ # define PACKED __attribute__ ((packed))
+-# if __GNUC__ == 2 && __GNUC_MINOR__ > 6 || __GNUC__ >= 3
++# if (__GNUC__ == 2 && __GNUC_MINOR__ > 6 || __GNUC__ >= 3) && !defined(__clang__)
+ /* gcc 2.6.3 doesn't have "unused" */		/* mool */
+ #  define UNUSED(x) x __attribute__ ((unused));x
+ #  define UNUSEDP __attribute__ ((unused))

meta/recipes-devtools/mtools/mtools_4.0.18.bb

@@ -32,6 +32,7 @@ SRC_URI = "${GNU_MIRROR}/mtools/mtools-${PV}.tar.bz2 \
            file://no-x11.gplv3.patch \
            file://0001-Continue-even-if-fs-size-is-not-divisible-by-sectors.patch \
            file://0001-remove-LOCK_NB-to-use-blocking-request.patch \
+           file://clang_UNUSED.patch \
            "
 
 SRC_URI_append_class-native = " file://disable-hardcoded-configs.patch"