Fix GCC (8.2.1) build error.

Not sure that I think this is a very valid build error from GCC, but
it's easy enough to work around.

../crypto/cpu-arm-linux_test.cc: In member function ‘virtual void ARMLinuxTest_CPUInfo_Test::TestBody()’:
../crypto/cpu-arm-linux_test.cc:25:10: error: declaration of ‘struct ARMLinuxTest_CPUInfo_Test::TestBody()::Test’ shadows a previous local [-Werror=shadow]
   struct Test {
          ^~~~
In file included from ../crypto/cpu-arm-linux_test.cc:19:
../third_party/googletest/include/gtest/gtest.h:375:23: note: shadowed declaration is here
 class GTEST_API_ Test {

Change-Id: Icc1676a621ec26b3665adaf5daf7d6c6f5307ba8
Reviewed-on: https://boringssl-review.googlesource.com/31624
Reviewed-by: Adam Langley <agl@google.com>

crypto/cpu-arm-linux_test.cc

@@ -22,7 +22,7 @@
 #if !defined(BORINGSSL_SHARED_LIBRARY)
 
 TEST(ARMLinuxTest, CPUInfo) {
-  struct Test {
+  struct CPUInfoTest {
     const char *cpuinfo;
     unsigned long hwcap;
     unsigned long hwcap2;