android_regen and Android.bp updates for 3.8.2

* Work around flaky Makefile regeneration that would wipe out our
  modification by touching some files and running `make Makefile` before
  making our changes.
* Support the generated lib/malloc/*.h headers
* Ignore the unused-parameter warning
* Move to C17, as upstream uses the compiler default.
* Switch musl regen to using the prebuilt sysroot
* Disable iconv and vfork on Mac

Change-Id: I5294bb3ae66a3ccd830503a802a5a536ba50d72f
2 files changed