kcov: don't profile branches in kcov

Profiling 'if' statements in __sanitizer_cov_trace_pc() leads to
unbound recursion and crash:

	__sanitizer_cov_trace_pc() ->
		ftrace_likely_update ->
			__sanitizer_cov_trace_pc() ...

Define DISABLE_BRANCH_PROFILING to disable this tracer.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kcov.c

@@ -1,5 +1,6 @@
 #define pr_fmt(fmt) "kcov: " fmt
 
+#define DISABLE_BRANCH_PROFILING
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <linux/file.h>