compiler-clang: remove version check for BPF Tracing

bpftrace parses the kernel headers and uses Clang under the hood.

Remove the version check when __BPF_TRACING__ is defined (as bpftrace
does) so that this tool can continue to parse kernel headers, even with
older clang sources.

Fixes: commit 1f7a44f ("compiler-clang: add build check for clang 10.0.1")
Reported-by: Chen Yu <yu.chen.surf@gmail.com>
Reported-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Jarkko Sakkinen <jarkko@kernel.org>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lkml.kernel.org/r/20201104191052.390657-1-ndesaulniers@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: nickdesaulniers

include/linux/compiler-clang.h

@@ -8,8 +8,10 @@
 		     + __clang_patchlevel__)
 
 #if CLANG_VERSION < 100001
+#ifndef __BPF_TRACING__
 # error Sorry, your version of Clang is too old - please use 10.0.1 or newer.
 #endif
+#endif
 
 /* Compiler specific definitions for Clang compiler */