tools: Add additional SYM_*() stubs to linkage.h

Similar to commit f8d92fc5 ("selftests: vDSO: fix include order in
build of test_vdso_chacha") add SYM_DATA_START, SYM_DATA_START_LOCAL, and
SYM_DATA_END stubs to tools/include/linux/linkage.h so that the proper
macros can be used within the kernel's vdso code as well as in the
vdso_test_chacha selftest.
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

tools/include/linux/linkage.h

@@ -2,7 +2,9 @@
 #define _TOOLS_INCLUDE_LINUX_LINKAGE_H
 
 #define SYM_FUNC_START(x) .globl x; x:
-
 #define SYM_FUNC_END(x)
+#define SYM_DATA_START(x) .globl x; x:
+#define SYM_DATA_START_LOCAL(x) x:
+#define SYM_DATA_END(x)
 
 #endif /* _TOOLS_INCLUDE_LINUX_LINKAGE_H */