Move NDK_TRIPLE handling outside of HERMETIC_TOOLCHAIN guard so that
build/config.sh doesn't reset CONFIG_UAPI_HEADER_TEST=y.

Test: BUILD_CONFIG=common/build.config.gki.aarch64 ./build/config.sh
Bug: 234853506
Suggested-by: Elliot Berman <eberman@quicinc.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: Ied0864c0f2c9e2364a0af1bfe54cecb12832aada