Travis-CI: for building using Clang, also set $Config{ld}

See "ld" in `perldoc Config`.

.travis.yml

@@ -36,7 +36,8 @@ before_install:
   - sudo apt-get install build-essential libx11-dev pgplot5 libplplot-dev libgd2-xpm-dev libhdf4-alt-dev libproj-dev libvpx-dev libxpm-dev proj-bin libcfitsio3-dev libreadline-dev
   - if [ "$DISABLE_FORTRAN" != 1 ]; then sudo apt-get install gfortran; fi # set DISABLE_FOTRAN = 1 to not install gfortran
   # clang is already installed in Travis-CI environment. Using PERL_MM_OPT does not work with subdirectory Makefile.PLs so we override Config.pm
-  - if [ "$CC" == "clang" ]; then mkdir build_aux; echo 'package force_clang; use ExtUtils::MakeMaker::Config; $Config{cc} = "clang"; 1' > build_aux/force_clang.pm; export PERL5OPT="-I$(pwd)/build_aux -Mforce_clang"; fi
+  # Also, both $Config{cc} and $Config{ld} need to be set because under ELF environments (such as Travis-CI's Ubuntu), this is what Perl's Config.pm does.
+  - if [ "$CC" == "clang" ]; then mkdir build_aux; echo 'package force_clang; use ExtUtils::MakeMaker::Config; $Config{cc} = $Config{ld} = "clang"; 1' > build_aux/force_clang.pm; export PERL5OPT="-I$(pwd)/build_aux -Mforce_clang"; fi
   - sudo apt-get install libxi-dev libxmu-dev freeglut3-dev libgsl0-dev libnetpbm10-dev # for OpenGL
   - export PGPLOT_DEV=/NULL
   - perl -pi -e 's|WITH_BADVAL => 1|WITH_BADVAL => 0|       if defined $ENV{PDL_WITH_BADVAL}    && $ENV{PDL_WITH_BADVAL}     == 0' perldl.conf # disable bad value support