Reland "Split the x86 host toolchain into glibc and musl variants"

Split the x86 host toolchain into glibc and musl variants

Create new musl toolchains that are based on the existing glibc
toolchains, and add the necessary flags for musl compiles.

This relands Ifc02f9e5afa61ff758be98b0c962f3a4b53d0546 with changes
for I46672e3a096b6ea94ff4c10e1c31e8fd010a163c.

Bug: 190084016
Change-Id: Iaa9f7a50ff601155ecd73acc5701a2c226be66dc
Test: TestArchMutator