Replace all occurrances of asm with __asm__ in the output headers

asm() conflicts with userland code compiled with -std=c99, the userland
libc should only use __asm__() instead. Therefore, this transformation
has to be applied to all exported headers.

This only changes arch-arm/asm/byteorder.h.

Change-Id: I1cf88c37201c3a91668d387293a18885c316d53c
diff --git a/libc/kernel/tools/clean_header.py b/libc/kernel/tools/clean_header.py
index 28cb05e..dad9120 100755
--- a/libc/kernel/tools/clean_header.py
+++ b/libc/kernel/tools/clean_header.py
@@ -71,6 +71,7 @@
     list.removeEmptyLines()
     list.removeMacroDefines( kernel_ignored_macros )
     list.insertDisclaimer( kernel.kernel_disclaimer )
+    list.replaceTokens( kernel_token_replacements )
 
     out = StringOutput()
     list.write(out)