WIP: Refactor CMake build system to more modular

cmake/cflags-ppc64le.cmake

@@ -0,0 +1,18 @@
+
+CHECK_INCLUDE_FILE_CXX(altivec.h HAVE_C_PPC64EL_ALTIVEC_H)
+
+if (HAVE_C_PPC64EL_ALTIVEC_H)
+    set (INTRIN_INC_H "altivec.h")
+else()
+    message (FATAL_ERROR "No intrinsics header found for VSX")
+endif ()
+
+CHECK_C_SOURCE_COMPILES("#include <${INTRIN_INC_H}>
+int main() {
+    vector int a = vec_splat_s32(1);
+    (void)a;
+}" HAVE_VSX)
+
+if (NOT HAVE_VSX)
+    message(FATAL_ERROR "VSX support required for Power support")
+endif ()