Cache compiler lookup per package (#23988)

Before:

```
$ hyperfine '~/spack/bin/spack -e . build-env rocfft'
Benchmark #1: ~/spack/bin/spack -e . build-env rocfft
  Time (mean ± σ):      1.593 s ±  0.016 s    [User: 1.468 s, System: 0.126 s]
  Range (min … max):    1.575 s …  1.628 s    10 runs
```

After:

```
$ hyperfine '~/spack/bin/spack -e . build-env rocfft'
Benchmark #1: ~/spack/bin/spack -e . build-env rocfft
  Time (mean ± σ):      1.407 s ±  0.020 s    [User: 1.280 s, System: 0.127 s]
  Range (min … max):    1.393 s …  1.455 s    10 runs
```

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/spack/spack/package.py b/lib/spack/spack/package.py
index 169958f704..9958f16efe 100644
--- a/lib/spack/spack/package.py
+++ b/lib/spack/spack/package.py
@@ -1269,11 +1269,13 @@ class PackageBase(six.with_metaclass(PackageMeta, PackageViewMixin, object)):
             raise ValueError("Can only get the arch for concrete package.")
         return spack.architecture.arch_for_spec(self.spec.architecture)
 
-    @property
+    @property  # type: ignore
+    @memoized
     def compiler(self):
         """Get the spack.compiler.Compiler object used to build this package"""
         if not self.spec.concrete:
             raise ValueError("Can only get a compiler for a concrete package.")
+
         return spack.compilers.compiler_for_spec(self.spec.compiler,
                                                  self.spec.architecture)