matplotlib: add dep on gmake when %gcc (spack#2526)

This is not meant to be a long term solution, but when there is no system installed make these packages fail to build. The issue is that gmake is a runtime dependency of GCC, but not modeled as such by Spack.

Signed-off-by: Ryan Krattiger <ryan.krattiger@kitware.com>

Author: kwryankrattiger

repos/spack_repo/builtin/packages/py_matplotlib/package.py

@@ -144,6 +144,11 @@ class PyMatplotlib(PythonPackage):
     depends_on("c", type="build")
     depends_on("cxx", type="build")
 
+    # This is required for the gcc lto wrapper which calls gmake
+    # Without this the spack installer doesn't know what to pass
+    # when building with the gnu jobserver
+    depends_on("gmake", type="build", when="%gcc")
+
     # https://matplotlib.org/stable/install/dependencies.html
     # Runtime dependencies
     # Mandatory dependencies