Set PWD to the absolute path of the top tree.
Set PWD to the absolute path of the top tree.

Previously PWD is passed in as a shell environmental variable,
which does not point to top of the source tree if you run mm/mmm.
That in turn breaks mm/mmm if OUT_DIR_COMMON_BASE is set to an absolute
path.

Change-Id: Iac99d5668aee1bbd3cb9897750afc2149bd9f973

xorware/android_build,xorware/android_build,xorware/android_build,hagar006/platform_manifest,xorware/android_build,knone1/platform_manifest,pranav01/platform_manifest,see4ri/lolili,RR-msm7x30/platform_manifest,xorware/android_build,Hybrid-Power/startsync,ND-3500/platform_manifest,fallouttester/platform_manifest