fix parmetis on Ubuntu with GNU compilers by linking to lm

var/spack/repos/builtin/packages/parmetis/link-to-lm.patch

@@ -0,0 +1,14 @@
+diff --git a/libparmetis/CMakeLists.txt b/libparmetis/CMakeLists.txt
+index 9cfc8a7..dfc0125 100644
+--- a/libparmetis/CMakeLists.txt
++++ b/libparmetis/CMakeLists.txt
+@@ -5,7 +5,7 @@ file(GLOB parmetis_sources *.c)
+ # Create libparmetis
+ add_library(parmetis ${ParMETIS_LIBRARY_TYPE} ${parmetis_sources})
+ # Link with metis and MPI libraries.
+-target_link_libraries(parmetis metis ${MPI_LIBRARIES})
++target_link_libraries(parmetis metis ${MPI_LIBRARIES} "-lm")
+ set_target_properties(parmetis PROPERTIES LINK_FLAGS "${MPI_LINK_FLAGS}")
+
+ install(TARGETS parmetis
+

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

@@ -52,6 +52,8 @@ class Parmetis(Package):
     # https://bitbucket.org/petsc/pkg-parmetis/commits/82409d68aa1d6cbc70740d0f35024aae17f7d5cb/raw/
     patch('pkg-parmetis-82409d68aa1d6cbc70740d0f35024aae17f7d5cb.patch')
 
+    patch('link-to-lm.patch')
+
     depends_on('gdb', when='+gdb')
 
     def install(self, spec, prefix):