Don't leak Android hacks to other build platforms.

Previously, android_compat_hacks.c and android_compat_keywrap.c
were added to crypto_sources when multiple build platforms were
specified in one invocation.

Change-Id: I4fd8bffc4785bef0148d12cd6f292d79c043b806
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
Reviewed-on: https://boringssl-review.googlesource.com/6566
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

util/generate_build_files.py

diff --git a/util/generate_build_files.py b/util/generate_build_files.py
index 288fe0e..4a78005 100644
--- a/util/generate_build_files.py
+++ b/util/generate_build_files.py
@@ -150,8 +150,8 @@
     with open('sources.mk', 'w+') as makefile:
       makefile.write(self.header)
 
-      files['crypto'].extend(self.ExtraFiles())
-      self.PrintVariableSection(makefile, 'crypto_sources', files['crypto'])
+      crypto_files = files['crypto'] + self.ExtraFiles()
+      self.PrintVariableSection(makefile, 'crypto_sources', crypto_files)
       self.PrintVariableSection(makefile, 'ssl_sources', files['ssl'])
       self.PrintVariableSection(makefile, 'tool_sources', files['tool'])