If the callee and caller use different calling convensions, we cannot apply TCO if the callee requires arguments on stack; e.g. C calling convention and Fast CC use the same registers for parameter passing, but the stack offset is not necessarily same.
Due to this problem, Brotli failed in make test on PowerPC.
This patch also recommit r319218 "[PowerPC] Allow tail calls of fastcc functions from C CallingConv functions." since the problem reported in r320106 should be fixed.