Update to llvm excludes assembly instructions.
llvm git revision is below
commit 65fad7c26569 ("bpf: add inline-asm support")
This change will be part of llvm release 6.0
__ASM_SYSREG_H define is not required for native compile.
-target switch includes appropriate target specific files
while cross compiling
Tested on x86 and arm64.
Signed-off-by: Abhijit Ayarekar <abhijit.ayarekar@xxxxxxxxxxxxxxxxxx>