Merge branch 'fix/petsc-deb9-ub1604' into 'master'

Add fix for PETSc detection on Debian 9/Ubuntu 16.04

This MR fixes a problem with detecting PETSc with later Debian/PETSc packages, which is currently preventing the Debian 9 buildbot from compiling properly.

See merge request !735

CHANGELOG.md

@@ -39,6 +39,7 @@ v4.4.0
 - Fix bug in the calculation of the RHS magnitude in CG solver (!721)
 - Fix bug in CMake Homebrew and MacPorts detection for OS X (!729)
 - Fix bug in FieldUtils when using half mode expansions (!734)
+- Fix bug in CMake PETSc detection for Ubuntu 16.04/Debian 9 (!735)
 
 **ADRSolver:**
 - Add a projection equation system for C^0 projections (!675)

cmake/FindPETSc.cmake

@@ -225,6 +225,13 @@ show :
   else ()
     set (PETSC_LIBRARY_VEC "NOTFOUND" CACHE INTERNAL "Cleared" FORCE) # There is no libpetscvec
     petsc_find_library (SINGLE petsc)
+    # Debian 9/Ubuntu 16.04 uses _real and _complex extensions when using libraries in /usr/lib/petsc.
+    if (NOT PETSC_LIBRARY_SINGLE)
+      petsc_find_library (SINGLE petsc_real)
+    endif()
+    if (NOT PETSC_LIBRARY_SINGLE)
+      petsc_find_library (SINGLE petsc_complex)
+    endif()
     foreach (pkg SYS VEC MAT DM KSP SNES TS ALL)
       set (PETSC_LIBRARIES_${pkg} "${PETSC_LIBRARY_SINGLE}")
     endforeach ()