Reland "bionic_libc_platform_headers is only available when building with Bionic".

Relanding unchanged - the build problem was due to a split topic.

Test: m checkbuild
Test: atest libunwindstack_unit_test
Test: lunch fvp-userdebug && mmm system/core/libunwindstack
Bug: 152255951
Change-Id: Ifd1ced65b840ef216630906eec1ec31233e0c5f1