Support building simpleperf against musl

Support building simpleperf against musl by including the missing
sys/time.h header and providing a definition of gettid, which
doesn't exist in musl.

Bug: 190084016
Test: m USE_HOST_MUSL=true host-native
Change-Id: Idcff0bf356ed2523dd953ddb6eba10c206afaa2b
2 files changed