Add package for fiat based on builtin but adding um as a version

[penguian]

Closes #147

This package is used by the um package to add DR_HOOK as per #148.

This package is based on the builtin package, with the following differences.

1. It uses the ACCESS-NRI/fiat repository.
2. It adds a "um" version that uses the "um" branch of ACCESS-NRI/fiat. This branch adds a modified version of DR_HOOK_DEFAULT that allows a communicator to be specified.
3. It does not patch the "um" version.
4. It adds "CMAKE_*_COMPILER" defines to cmake_args so that CMake can find the mpifc compiler, etc.

$ diff -U0 -w spack/var/spack/repos/builtin/packages/fiat/package.py spack-packages/packages/fiat/package.py 
--- spack/var/spack/repos/builtin/packages/fiat/package.py	2024-09-25 09:25:23.000000000 +1000
+++ spack-packages/packages/fiat/package.py	2024-09-25 10:05:27.000000000 +1000
@@ -5,0 +6,2 @@
+# Based on spack/var/spack/repos/builtin/packages/fiat/package.py
+
@@ -14 +16 @@
-    git = "https://github.com/ecmwf-ifs/fiat.git"
+    git = "https://github.com/ACCESS-NRI/fiat.git"
@@ -17 +19 @@
-    maintainers("climbfuji")
+    maintainers("climbfuji", "penguian")
@@ -21,0 +24 @@
+    version("um", branch="um", no_cache=True)
@@ -42 +45 @@
-    patch("intel_warnings_v110.patch", when="@:1.1.0")
+    patch("intel_warnings_v110.patch", when="@0:1.1.0")
@@ -51 +54,8 @@
-
+        if "+mpi" in self.spec:
+            args.extend(
+                [
+                    self.define("CMAKE_C_COMPILER", self.spec["mpi"].mpicc),
+                    self.define("CMAKE_CXX_COMPILER", self.spec["mpi"].mpicxx),
+                    self.define("CMAKE_Fortran_COMPILER", self.spec["mpi"].mpifc),
+                ]
+            )

[harshula]

When built with @um does Spack consider that version to be less than 1.1.0?

[penguian]

When built with @um does Spack consider that version to be less than 1.1.0?

Yes. I was expecting that it would be greater than 1.2.0, but it doesn't work that way: "String components are considered less than numeric components" so "um" < "0". Special string components are an exception.