Add snowflake pt to alpha linux builds
Please see the attached. Reproducibility of cgo depends on a compiler that supports, ``` -gno-record-gcc-switches -fdebug-prefix-map=$WORK=/tmp/go-build ``` which landed in go 1.7.3 (see https://github.com/golang/go/commit/5bbb98df0960f57dca73cb7640456608d4cc0917)
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