Tried to reinstall a package with spack install --overwrite and it failed to find "cmake" which was a build dependency.

This happens with either concretizer turned on.

Steps to reproduce the issue

• Make sure you do not have "cmake" in your path.
• fresh install of spack v0.16.1
• Install mysql (if you don't have it already)
• Try to re-install mysql with --overwrite

$ which cmake
/usr/bin/which: no cmake in (...)
$ spack install mysql@5.7.27
...
$ spack find --long mysql
==> 1 installed package
-- linux-scientific7-ivybridge / gcc@4.8.5 ----------------------
xhxn7te mysql@5.7.27

$ spack install --overwrite mysql/xhxn7te    # hash from above
==> The following package specs will be reinstalled:

-- linux-scientific7-x86_64 / gcc@9.3.0 -------------------------
euf24m3 mysql@8.0.19%gcc +client_only~ipo build_type=RelWithDebInfo cxxstd=17
==> Do you want to proceed? [y/N] y
...
==> mysql: Executing phase: 'cmake'
==> Error: ProcessError: cmake: No such file or directory
...

So in the plain "spack install" case, it did find add cmake to the build environment
but in the --overwrite case it didn't.

You can work around this by "spack load"-ing the build dependencies before doing
the spack install --overwrite in the case of cmake, but this doesn't solve all build
dependency issues.

Information on your system

$ spack debug report

• Spack: 0.16.1
• Python: 3.6.8
• Platform: linux-scientific7-ivybridge

Additional information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have searched the issues of this repo and believe this is not a duplicate
• I have run the failing commands in debug mode and reported the output debug_out.txt