Emit #if guards for ARM assembly files.

This change causes the generated assembly files for ARM and AArch64 to
have #if guards for __arm__ and __aarch64__, respectively. Since
building on ARM is only supported for Linux, we only have to worry about
GCC/Clang's predefines.

Change-Id: I7198eab6230bcfc26257f0fb6a0cc3166df0bb29
Reviewed-on: https://boringssl-review.googlesource.com/5173
Reviewed-by: Adam Langley <agl@google.com>

crypto/chacha/chacha_vec_arm.S

diff --git a/crypto/chacha/chacha_vec_arm.S b/crypto/chacha/chacha_vec_arm.S
index ddc374e..0f82627 100644
--- a/crypto/chacha/chacha_vec_arm.S
+++ b/crypto/chacha/chacha_vec_arm.S
@@ -23,6 +23,7 @@
 #     /opt/gcc-linaro-4.9-2014.11-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc -O3 -mcpu=cortex-a8 -mfpu=neon -fpic -DASM_GEN -I ../../include -S chacha_vec.c -o -
 
 #if !defined(OPENSSL_NO_ASM)
+#if defined(__arm__) || defined(__aarch64__)
 
 	.syntax unified
 	.cpu cortex-a8
@@ -1423,4 +1424,5 @@
 	.ident	"GCC: (Linaro GCC 2014.11) 4.9.3 20141031 (prerelease)"
 	.section	.note.GNU-stack,"",%progbits
 
+#endif  /* __arm__ || __aarch64__ */
 #endif  /* !OPENSSL_NO_ASM */

crypto/chacha/chacha_vec_arm_generate.go

diff --git a/crypto/chacha/chacha_vec_arm_generate.go b/crypto/chacha/chacha_vec_arm_generate.go
index d681e8a..6d167b9 100644
--- a/crypto/chacha/chacha_vec_arm_generate.go
+++ b/crypto/chacha/chacha_vec_arm_generate.go
@@ -52,7 +52,8 @@
 	output.WriteString(compiler)
 	output.WriteString(" ")
 	output.WriteString(strings.Join(args, " "))
-	output.WriteString("\n\n#if !defined(OPENSSL_NO_ASM)\n\n")
+	output.WriteString("\n\n#if !defined(OPENSSL_NO_ASM)\n")
+	output.WriteString("#if defined(__arm__) || defined(__aarch64__)\n\n")
 
 	cmd := exec.Command(compiler, args...)
 	cmd.Stderr = os.Stderr
@@ -144,5 +145,6 @@
 `
 
 const trailer = `
+#endif  /* __arm__ || __aarch64__ */
 #endif  /* !OPENSSL_NO_ASM */
 `

crypto/perlasm/arm-xlate.pl

diff --git a/crypto/perlasm/arm-xlate.pl b/crypto/perlasm/arm-xlate.pl
index 81ceb31..706fa70 100755
--- a/crypto/perlasm/arm-xlate.pl
+++ b/crypto/perlasm/arm-xlate.pl
@@ -116,6 +116,9 @@
     return $line;
 }
 
+print "#if defined(__arm__)\n" if ($flavour eq "linux32");
+print "#if defined(__aarch64__)\n" if ($flavour eq "linux64");
+
 while($line=<>) {
 
     if ($line =~ m/^\s*(#|@|\/\/)/)	{ print $line; next; }
@@ -162,4 +165,6 @@
     print "\n";
 }
 
+print "#endif" if ($flavour eq "linux32" || $flavour eq "linux64");
+
 close STDOUT;