samples/bpf: Add a workaround for asm_inline

This was added in commit eb111869 ("compiler-types.h: add asm_inline
definition") and breaks samples/bpf as clang does not support asm __inline.

Fixes: eb111869 ("compiler-types.h: add asm_inline definition")
Co-developed-by: Florent Revest <revest@google.com>
Signed-off-by: Florent Revest <revest@google.com>
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191002191652.11432-1-kpsingh@chromium.org

samples/bpf/asm_goto_workaround.h

@@ -3,7 +3,8 @@
 #ifndef __ASM_GOTO_WORKAROUND_H
 #define __ASM_GOTO_WORKAROUND_H
 
-/* this will bring in asm_volatile_goto macro definition
+/*
+ * This will bring in asm_volatile_goto and asm_inline macro definitions
  * if enabled by compiler and config options.
  */
 #include <linux/types.h>
@@ -13,5 +14,15 @@
 #define asm_volatile_goto(x...) asm volatile("invalid use of asm_volatile_goto")
 #endif
 
+/*
+ * asm_inline is defined as asm __inline in "include/linux/compiler_types.h"
+ * if supported by the kernel's CC (i.e CONFIG_CC_HAS_ASM_INLINE) which is not
+ * supported by CLANG.
+ */
+#ifdef asm_inline
+#undef asm_inline
+#define asm_inline asm
+#endif
+
 #define volatile(x...) volatile("")
 #endif