[arch][riscv] C++ header guard the core riscv header
#ifndef ASSEMBLY
#define __ASM_STR(x) #x
+__BEGIN_CDECLS
+
#define riscv_csr_clear(csr, bits) \
({ \
ulong __val = bits; \
@@ -238,4 +240,6 @@ static inline uint64_t riscv_get_time(void) {
# endif
#endif
+__END_CDECLS
+
#endif /* ASSEMBLY */
