Build: Set FLOATTEST* by default for AArch64, PPC Because of 47656a082091f9c9efda054674522513f4768c6c, we can now reliably determine the correct default values for FLOATTEST8 and FLOATTEST12 when using Clang or GCC to build for AArch64 or PowerPC platforms. (Testing confirms that this is the case with GCC 5-13 and Clang 5-14 on Ubuntu/AArch64, GCC 4 on CentOS 7/PPC, and GCC 8-10 and Clang 6-12 on Ubuntu/PPCLE.) Other CPU architectures and compilers can be added on a case-by-case basis as they are tested.