[compiler-rt] [Arm] Make the tests for the runtime functions __aeabi_c{d,f} work on Big-Endian.

We are trying to build the compiler-rt as big-endian. And found that the tests compiler-rt/test/builtins/Unit/arm/aeabi_cdcmpeq_test.c and compiler-rt/test/builtins/Unit/arm/aeabi_cfcmpeq_test.c do not work on big endian at the moment. This patch makes these tests work on big endian as well.

Reviewed By: peter.smith, simon_tatham

Differential Revision: https://reviews.llvm.org/D155208