[ulib][musl] Initialize a variable to silence a warning

GCC 7 for arm64 (but not for x64) cites this as "maybe uninitialized"
even though the code logic means it never can be. Just zero it anyway.

Change-Id: I5f1ebc7638fc8199d8d2d14ffaf6b45d7b29dd1d

[musl] Clean up some warnings in musl's make build

Change-Id: Ib305f1d161634156fad8f7303208c49be66c855c

[musl] clang format musl

Change-Id: I3bc6ab7655410514691cd07f08454f3afd41d9b3

[magenta] Initial commit