Fix targets configuration when PETSc or SLEPc are not installed

CMakeLists.txt

@@ -178,6 +178,7 @@ if (PUGS_ENABLE_PETSC MATCHES "^(AUTO|ON)$")
     # PETSc support is deactivated if MPI is not found
     pkg_check_modules(PETSC IMPORTED_TARGET GLOBAL PETSc)
 
+    if (${PETSC_FOUND})
       set_property(TARGET PkgConfig::PETSC PROPERTY
 	IMPORTED_LOCATION "${PETSC_LIBRARIES}"
       )
@@ -186,6 +187,7 @@ if (PUGS_ENABLE_PETSC MATCHES "^(AUTO|ON)$")
       )
 
       set(PETSC_TARGET PkgConfig::PETSC)
+    endif()
   else()
     message(STATUS "PETSc support is deactivated since pugs will not be build with MPI support")
     set(PETSC_FOUND FALSE)
@@ -215,6 +217,7 @@ if (PUGS_ENABLE_SLEPC MATCHES "^(AUTO|ON)$")
     # SLEPc support is deactivated if PETSc is not found
     pkg_check_modules(SLEPC IMPORTED_TARGET GLOBAL SLEPc)
 
+    if (${SLEPC_FOUND})
       set_property(TARGET PkgConfig::SLEPC PROPERTY
 	IMPORTED_LOCATION "${SLEPC_LIBRARIES}"
       )
@@ -223,6 +226,7 @@ if (PUGS_ENABLE_SLEPC MATCHES "^(AUTO|ON)$")
       )
 
       set(SLEPC_TARGET PkgConfig::SLEPC)
+    endif()
   else()
     message(STATUS "SLEPc support is deactivated since pugs will not be build with PETSc support")
     set(SLEPC_FOUND FALSE)