Remove more BSD cruft from the public headers.

Change-Id: I1e3097f745b526db448bf72fbc05fb2ba23929a0
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 6f238a9..21d59fa 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -77,7 +77,9 @@
 #define	__GNUC_PREREQ(x, y)	0
 #endif
 
-#include <sys/cdefs_elf.h>
+#define __strong_alias(alias, sym) \
+    __asm__(".global " #alias "\n" \
+            #alias " = " #sym);
 
 #if defined(__cplusplus)
 #define	__BEGIN_DECLS		extern "C" {
@@ -263,13 +265,6 @@
 #endif
 #endif /* !(__STDC_VERSION__ >= 199901L) */
 
-#if defined(_KERNEL)
-#if defined(NO_KERNEL_RCSIDS)
-#undef __KERNEL_RCSID
-#define	__KERNEL_RCSID(_n, _s)		/* nothing */
-#endif /* NO_KERNEL_RCSIDS */
-#endif /* _KERNEL */
-
 /*
  * A barrier to stop the optimizer from moving code or assume live
  * register values. This is gcc specific, the version is more or less