bp2build: remove libc_tzcode from denylist.

This now works with --features no_copts_tokenization. With tokenization,
the escaped empty string '\"\"' became an actual empty string '' on the
command line, setting -DWILDABBR to the wrong value.

However, no_copts_tokenization unveiled other problems with Android.bp
flags, such as spaces in existing cflags like
https://cs.android.com/android/platform/superproject/+/master:bionic/libc/Android.bp;l=288;drc=a0a4a6c2967b5b3c02c951ea1145f32ed5564ab9
- this trips up Bazel's copts when generated literally, so the
fix (other than splitting on space and making Soong accept strings that
don't start with dashes as cflags) is to make bp2build split cflags on
spaces before generating them as copts.

Test: bp2build, build bionic/...
Fixes: 186822591
Change-Id: Icf10bd20f6fb81db0b719ca0555fc70c75b91a79