[tests] filter out pwd path prefix in clang error messages

Now that we use more systematically the Filepath.Normalized version of
filenames, this shows in clang messages as absolute filenames in location.
To have reproducible oracles, the pwd component must be filtered out.

tests/bugs/test_config

 FILEREG:.*\.\(cc\|cpp\|ii\)$
 MACRO: CXX -machdep=x86_64 -cxx-c++stdlib-path share/libc++ -cxx-clang-command="bin/framaCIRGen -target x86_64-linux-gnu -D__FC_MACHDEP_X86_64"
 OPT:-print -wp -wp-msg-key="no-time-info,no-step-info" -wp-cache none  @CXX@
-FILTER:/bin/sed -e '/^#[^\n]*/d' -e "s|${FRAMAC_SHARE}|FRAMAC_SHARE|g" -e 's/Alt-Ergo [0-9.]\+/Alt-Ergo/'
+FILTER:/bin/sed -e '/^#[^\n]*/d' -e "s|${FRAMAC_SHARE}|FRAMAC_SHARE|g" -e 's/Alt-Ergo [0-9.]\+/Alt-Ergo/' -e "s|$(pwd)/||g"

tests/test_config

@@ -2,5 +2,5 @@ FILEREG:.*\.\(cc\|cpp\|ii\)$
 MACRO: CXX -cxx-c++stdlib-path share/libc++ -cxx-clang-command="bin/framaCIRGen"
 MACRO: EVA -eva -eva-msg-key=-summary
 OPT:-print -check @CXX@
-FILTER:/bin/sed  -e "s|${FRAMAC_SHARE}|FRAMAC_SHARE|g"
+FILTER:/bin/sed  -e "s|${FRAMAC_SHARE}|FRAMAC_SHARE|g" -e "s|$(pwd)/||g"
 ##FILTER:/bin/sed -e '/^#[^\n]*/d' -e "s|${FRAMAC_SHARE}|FRAMAC_SHARE|g"