Spack compiler wrappers are ignored with blt 0.7.0

[pearce8]

When building hip codes with blt 0.7.0, the spack compiler wrappers are ignored.

@scheibelp's current take is that blt is doing things appropriately because for recent rocm versions, the hip compiler doesn't delegate to anything (it did before, and that was spack's opportunity to shim in the spack compiler wrapper). So this change in behavior in blt 0.7.0 is actually it doing something correctly.