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

libc/kernel/tools/clean_header.py

@@ -71,6 +71,7 @@ def  cleanupFile( path ):
     list.removeEmptyLines()
     list.removeMacroDefines( kernel_ignored_macros )
     list.insertDisclaimer( kernel.kernel_disclaimer )
+    list.replaceTokens( kernel_token_replacements )
 
     out = StringOutput()
     list.write(out)

libc/kernel/tools/defaults.py

@@ -43,6 +43,11 @@ kernel_default_arch_macros = {
     "x86": {"__i386__": "1"},
     }
 
+# Replace tokens in the output according to this mapping
+kernel_token_replacements = {
+    {"asm": "__asm__"},
+    }
+
 # this is the set of known static inline functions that we want to keep
 # in the final ARM headers. this is only used to keep optimized byteswapping
 # static functions and stuff like that.