Fix veclibfort for gcc (#4548)

* fixes #967

* Version bump to 0.9.1

- Bugfixes for spack find
- 0.9.1 can read specs from current develop.

* Don't assume spack is in the path when building docs.

* fixing Makefile override of PREFIX and install w/gcc-6

var/spack/repos/builtin/packages/veclibfort/package.py

@@ -55,8 +55,16 @@ def install(self, spec, prefix):
         if sys.platform != 'darwin':
             raise InstallError('vecLibFort can be installed on macOS only')
 
-        make('all')
-        make('PREFIX=%s' % prefix, 'install')
+        filter_file(r'^PREFIX=.*', '', 'Makefile')
+
+        make_args = []
+
+        if spec.satisfies('%gcc@6:'):
+            make_args += ['CFLAGS=-flax-vector-conversions']
+
+        make_args += ['PREFIX=%s' % prefix, 'install']
+
+        make(*make_args)
 
         # test
         fc = which('fc')