Updates crosvm build script to be more local friendly

Apply the manual update to the gbm.pc file only once by checking
for exact line match.

Apply the manual update to the virglrenderer meson.build file
once so that the script works for the '_retry' commands.

Updates manifest copy to not require that the manifest file
be under $HOME and use full path.

Remove hardcoded directory accidentally introduced in aosp/1179683.

Updates script to only edit global git config if username isn't
detected.

Test: rebuild.sh (to rebuild once on GCE)
Test: rebuild_gce.sh (to rebuild once locally)

Change-Id: Ie5740d6e155d447e33f3a1dc64b8572410b176e1
2 files changed