Make Bazel always build with --fat_apk_cpu.

Also tweak the Android NDK CROSSTOOL file a bit so that it actually works.

Fixes #335.

--
MOS_MIGRATED_REVID=99377509

tools/cpp/BUILD

diff --git a/tools/cpp/BUILD b/tools/cpp/BUILD
index 240dc97..6599bc2 100644
--- a/tools/cpp/BUILD
+++ b/tools/cpp/BUILD
@@ -26,6 +26,7 @@
 filegroup(
     name = "toolchain",
     srcs = [
+        ":cc-compiler-armeabi-v7a",
         ":cc-compiler-darwin",
         ":cc-compiler-local",
         ":empty",
@@ -47,6 +48,20 @@
 )
 
 cc_toolchain(
+    name = "cc-compiler-armeabi-v7a",
+    all_files = ":empty",
+    compiler_files = ":empty",
+    cpu = "local",
+    dwp_files = ":empty",
+    dynamic_runtime_libs = [":empty"],
+    linker_files = ":empty",
+    objcopy_files = ":empty",
+    static_runtime_libs = [":empty"],
+    strip_files = ":empty",
+    supports_param_files = 0,
+)
+
+cc_toolchain(
     name = "cc-compiler-k8",
     all_files = ":empty",
     compiler_files = ":empty",