Add gcom4 package

[penguian]

Closes Issue #68 . See that issue for a description of the change requested.

This package applies patches to files in https://github.com/ACCESS-NRI/GCOM/tree/dev/Share/gcom4.5_access_config
as per https://github.com/coecms/access-esm-build-gadi/blob/master/Makefile rather than relying on updating the upstream repository.

The package has been tested to the point where the install completes.

[penguian]

I could add the following to package.py but have chosen not to at the moment:

1. Ensure that the dependent fcm executable is at the head of $PATH :

    def setup_build_environment(self, env):
        env.prepend_path("PATH", self.spec["fcm"].prefix.bin)

2. Alternatively, use the fcm executable defined by join_path(spec["fcm"].prefix.bin, "fcm")):

    def install(self, spec, prefix):

        def make_executable(spec, name):
            return Executable(join_path(spec[name].prefix.bin, name))

        fcm = make_executable(spec, "fcm")
        ...

But I would rather submit the package as-is, and debate the merits of such changes later.

Also, I would like to set the default compiler to "%intel" but I understand that this is not necessary.

[harshula]

Hi @penguian , Are there more changes planned for the patch() function?

[penguian]

@harshula I have made my changes and the PR is again ready for review.