Remove singularity build gcc warnings.
At the moments when building py2 using singularity we must ignore these warnings:
-Wno-cast-function-type -Wno-unused-command-line-argument -Wno-unknown-warning-option -Wno-unused-function -Wno-implicit-fallthrough
For py3 we ignore these warnings:
-Wno-unknown-pragmas -Wno-sign-compare
We should work on successfully building gstlal-spiir without settings these.