Use separate build directory for gzip (#14994)
Use separate build directory for gzip (#14994)

* Use separate build directory for gzip

At least on mac systems (perhaps because of a case sensitivity issue?)
gzip fails to build inside the source tree:
```
config.status: linking /var/folders/fy/x2xtwh1n7fn0_0q2kk29xkv9vvmbqb/T/spack-stage/s3j/spack-stage-gzip-1.10-iatwtuk2l5xgwmuh4pwu5bf27yezpydj/spack-src/GNUmakefile to GNUmakefile
config.status: executing depfiles commands
==> Executing phase: 'build'
==> [2020-02-14-09:32:45.502913] 'make' '-j12'
make: GNUmakefile: Too many levels of symbolic links
make: stat: GNUmakefile: Too many levels of symbolic links
make: *** No rule to make target `GNUmakefile'.  Stop.
```

* Simplify build directory and add gmake dependency

LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack