Small fixes for environment variables.

Fix all of the leaking of local variables by marking locals properly.

Fix a case where ANDROID_TOOLCHAIN_2ND_ARCH is set incorrectly.

Test: lunch'd aosp_angler-userdebug and then aosp_fugu-userdebug
Test: and verified ANDROID_TOOLCHAIN_2ND_ARCH is set properly after
Test: the first lunch and unset after the second lunch.
Test: Also attempt to build the two targets.
Change-Id: I49548e0d6654bfb1105a6ecaf2705825b9ddf3a5