Fix broken nacl build

Without this change the build fails due to direct use of ld rather then gcc/g++:

/usr/local/google/home/sbc/nacl_sdk/pepper_canary//toolchain/linux_x86_glibc/bin/x86_64-nacl-strip -x lib/libgtest.a
/usr/local/google/home/sbc/nacl_sdk/pepper_canary//toolchain/linux_x86_glibc/bin/x86_64-nacl-ld  -melf64_nacl -o bin/regaltest tmp/nacl-64/regal_tests/static/test_main.o tmp/nacl-64/regal_tests/static/testRegalTexC.o tmp/nacl-64/regal_tests/static/testRegalPixelConversions.o tmp/nacl-64/regal_tests/static/testStringList.o -lstdc++ -lpthread -ldl -lm -Llib -lgtest -lRegal -lm -ldl  -Llib -lpng -lz
/usr/local/google/home/sbc/nacl_sdk/pepper_canary//toolchain/linux_x86_glibc/bin/x86_64-nacl-ld: warning: cannot find entry symbol _start; defaulting to 0000000001002a40
tmp/nacl-64/regal_tests/static/test_main.o: In function `global constructors keyed to test_main.cpp':
test_main.cpp:(.text+0x62): undefined reference to `__dso_handle'
tmp/nacl-64/regal_tests/static/test_main.o: In function `testing::internal::TestFactoryImpl<(anonymous namespace)::DemoTest_DoesTestFrameworkWork_Test>::CreateTest()':
test_main.cpp:(.text+0x1dc): undefined reference to `_Unwind_Resume'
tmp/nacl-64/regal_tests/static/test_main.o: In function `(anonymous namespace)::DemoTest_DoesTestFrameworkWork_Test::TestBody()':
test_main.cpp:(.text+0x91c): undefined reference to `_Unwind_Resume'