package/ltp-testsuite: refine architecture dependency

As stated in commit [1], sparc toolchains doesn't have
any of __sync_*() family of functions implementation.

When __sync_add_and_fetch() is missing, ltp fallback to a local
implementation of tst_atomic_add_return() specific for each
supported architecture.
But there is none for sparc.

So add a dependency on BR2_TOOLCHAIN_HAS_SYNC_4 except for
architectures where a specific implementation is provided
in ltp-testsuite.

Fixes:
http://autobuild.buildroot.net/results/d7c/d7c3b145a64ed3916b89ddb4090050f3b9205e37

[1] 6856e417da4f3aa77e2a814db2a89429af072f7d

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/ltp-testsuite/Config.in

@@ -1,6 +1,15 @@
 config BR2_PACKAGE_LTP_TESTSUITE_ARCH_SUPPORTS
 	bool
-	default y
+	# Needs __sync*() built-ins for 4-byte data, except on a few
+	# architectures for which a specific implementation is
+	# provided in ltp-testsuite
+	default y if BR2_TOOLCHAIN_HAS_SYNC_4
+	default y if BR2_arc
+	default y if BR2_i386
+	default y if BR2_powerpc
+	default y if BR2_powepc64
+	default y if BR2_powerpc64le
+	default y if BR2_x86_64
 	# does not build on nios2, cachectl.h issue
 	depends on !BR2_nios2