trusty:libc: build explicit_bzero() into the library.

explicit_bzero() was added to musl in around 2020, but the extra source
file looked to hve been missed from rules.mk, making it unusable.  Add
this file so the function can be used.

Bug: 272549050
Test: build.py --test com.android.kernel.libctest
Change-Id: I0526ae8a42d39e3d7055daa225f1eef34024f07a
1 file changed