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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