[test][bugfix] Activate fvectortest with GMPField

Before the test was not active since '#if HAVE_GMP' fails
if the gmp-flags where not added.

dune/common/test/CMakeLists.txt

@@ -98,6 +98,7 @@ target_link_libraries("testfloatcmp" "dunecommon")
 add_executable("fmatrixtest" fmatrixtest.cc dummy.f)
 target_link_libraries("fmatrixtest" "dunecommon")
 add_executable("fvectortest" fvectortest.cc)
+add_dune_gmp_flags("fvectortest")
 add_executable("gcdlcmtest" gcdlcmtest.cc)
 add_executable("genericiterator_compile_fail" EXCLUDE_FROM_ALL genericiterator_compile_fail.cc)
 add_executable("integersequence" integersequence.cc)