Android: Fix building secondary arch in mixed 32/64-bit builds

Android: Fix building secondary arch in mixed 32/64-bit builds

TARGET_CC is not defined for the secondary arch on combined 32/64-bit
builds. The build system uses 2ND_TARGET_CC instead and it is not meant
to be used in module makefiles. LOCAL_CC was used to provide C only
flags as -std=c99 is not valid for C++ files. Since Android 4.4,
LOCAL_CONLYFLAGS was added to set compiler flags on C files only, so it
can be used now instead of LOCAL_CC.

This will break on pre-4.4 versions of Android, but it unlikely anyone
is using current Mesa with such an old version of Android.

Cc: Chih-Wei Huang <cwhuang@android-x86.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>