petsc4py: workaround LDSHARED change in 3cc5b7adc7 (#21541)

var/spack/repos/builtin/packages/py-petsc4py/ldshared.patch

@@ -0,0 +1,13 @@
+diff --git a/conf/baseconf.py b/conf/baseconf.py
+index 8a2466a5bd..73c08b923a 100644
+--- a/conf/baseconf.py
++++ b/conf/baseconf.py
+@@ -211,7 +211,7 @@ class PetscConfig:
+         ldshared = getenv('LDSHARED', ldshared)
+         ldflags = getenv('LDFLAGS', cflags + ' ' + (ldflags or ''))
+         ldcmd = split_quoted(ld) + split_quoted(ldflags)
+-        ldshared = [flg for flg in split_quoted(ldshared) if flg not in ldcmd]
++        ldshared = [flg for flg in split_quoted(ldshared) if flg not in ldcmd and (flg.find('/lib/spack/env')<0)]
+         ldshared = str.join(' ', ldshared)
+         #
+         def get_flags(cmd):

var/spack/repos/builtin/packages/py-petsc4py/package.py

@@ -31,6 +31,8 @@ class PyPetsc4py(PythonPackage):
 
     variant('mpi', default=True,  description='Activates MPI support')
 
+    patch('ldshared.patch')
+
     depends_on('py-cython', type='build', when='@develop')
     depends_on('python@2.6:2.8,3.3:', type=('build', 'run'))
     depends_on('py-setuptools', type='build')