Adapt "cross compile?" check for Apple Silicon

This piece of code tries to implement the semantics "cross compile?" to
determine CFLAGS used for test binary compilation.
```
if(ANDROID OR ${arch} MATCHES "arm|aarch64|riscv32|riscv64")
```

Since Apple Silicon, macOS runs on arm64e, so we take the wrong branch
when compiling and running tests locally "on the host" on an AS machine.

Furthermore, for Apple code, we use the separate
`get_test_cflags_for_apple_platform` function to determine these test
compiliation flags and `get_test_cc_for_arch` is only ever used in the
"compile & run on host" case, so we can short-curcuit the "cross
compile?" check here.

rdar://91446703

Differential Revision: https://reviews.llvm.org/D123633

compiler-rt/cmake/config-ix.cmake

@@ -244,7 +244,7 @@ endfunction()
 # specific architecture.  When cross-compiling, this is controled via
 # COMPILER_RT_TEST_COMPILER and COMPILER_RT_TEST_COMPILER_CFLAGS.
 macro(get_test_cc_for_arch arch cc_out cflags_out)
-  if(ANDROID OR ${arch} MATCHES "arm|aarch64|riscv32|riscv64")
+  if(ANDROID OR (NOT APPLE AND ${arch} MATCHES "arm|aarch64|riscv32|riscv64"))
     # This is only true if we are cross-compiling.
     # Build all tests with host compiler and use host tools.
     set(${cc_out} ${COMPILER_RT_TEST_COMPILER})