fixup! Use FVP models to test AArch64 Big Endian Variants.

Multilib flags do not need to have -mbig-endian.
Big endian variants can be differentiated with the target
aarch64_be. if the commandline options contain aarch64 and
-mbig-endian, clang convert the target into aarch64_be
already so that case works in that way. If the multilib
flags contain -mbig-endian, commandline options just
contain target=aarch64_be does not work, looks like multiib
system insist on having -mbig-endian in the commandline.

Author: simpal01

CMakeLists.txt

@@ -1647,7 +1647,7 @@ add_library_variants_for_cpu(
 add_library_variants_for_cpu(
     aarch64a_be
     COMPILE_FLAGS "--target=aarch64_be-unknown-none-elf -mbig-endian"
-    MULTILIB_FLAGS "--target=aarch64_be-unknown-none-elf -mbig-endian"
+    MULTILIB_FLAGS "--target=aarch64_be-unknown-none-elf"
     PICOLIBC_BUILD_TYPE "release"
     EXECUTOR fvp
     FVP_MODEL aem-a