Although the information you provide (what do you compile, what is the complete commandline..?) is rather sparse, that particular error looks like gcc cannot find one of its sub-tools (probably g++). Remember that gcc is only a frontend which delegates the actual work of compiling, assembling, and linking to a number of other tools (which are part of the gcc package). A
_spawnv error suggests that one of these is not good.
You use a custom build from a development snapshot of an alpha-stage compiler... need I say more
Very likely, some random component of the compiler is not in the right place (for whatever reason), and it will probably work fine if you use a clean installation.
