Fix building host valgrind for TARGET_ARCH=x86

The entire valgrind build was disabled when TARGET_ARCH=x86.  It
should still build the host valgrind tool even if the target arch
is not supported.  Use LOCAL_MODULE_TARGET_ARCH instead of a
conditional.

Test: lunch aosp_x86-eng && m checkbuild
Change-Id: I89de9f9675d30ea3a760339798ed41bc3eaa72c3
2 files changed