perl-5.12.1: Disable tests for PDL

We have a single failed test for PDL because of missing "pngtopnm".
Disable tests for this module.

perl-5.12.1-0.build.sh

@@ -394,11 +394,26 @@ cpan Object::Accessor
 cpan Object::Realize::Later
 cpan PDF::API2
 
+# PDL
 #
 # seems to fail (sometimes) with parallel builds during install:
 #  can't write to symdb /dev/shm/perl-5.28.1-0/lib/site_perl/5.28.1/x86_64-linux/PDL/pdldoc.db at blib/lib/PDL/Doc.pm line 497.
+# disabled parallel build
 #
-MAKEFLAGS= cpan PDL
+# Also one test fails:
+#    Oops, this is not a PNM fileconverter error: sh: pngtopnm: command not found
+#     at /dev/shm/perl-5.12.1-0.build.tmp/home/.cpan/build/PDL-2.021-0/blib/lib/PDL/IO/Pnm.pm line 79.
+#            PDL::IO::Pnm::rbarf("/dev/shm/perl-5.12.1-0.build.tmp/xx7fgrpX1_", "Oops, this is not a PNM file") called at /dev/shm/perl-5.12.1-0.build.tmp/home/.cpan/build/PDL-2.021-0/blib/lib/PDL/IO/Pnm.pm line 274
+#            PDL::rpnm("PDL", PDL=SCALAR(0x9115a0), "pngtopnm  \"/dev/shm/perl-5.12.1-0.build.tmp/o1iV1Ham33/t byte"...) called at /dev/shm/perl-5.12.1-0.build.tmp/home/.cpan/build/PDL-2 .021-0/blib/lib/PDL/IO/Pnm.pm line 248
+#            PDL::IO::Pnm::rpnm(PDL=SCALAR(0x9115a0), "pngtopnm  \"/dev/shm/perl-5.12.1-0.build.tmp/o1iV1Ham33/t byte"...) called at /dev/shm/perl-5.12.1-0.build.tmp/home/.cpan/build/PDL -2.021-0/blib/lib/PDL/IO/Pic.pm line 322
+#            PDL::rpic("PDL", "/dev/shm/perl-5.12.1-0.build.tmp/o1iV1Ham33/t byte_a.png") called at /dev/shm/perl-5.12.1-0.build.tmp/home/.cpan/build/PDL-2.021-0/blib/lib/PDL/IO/Pic.pm line 277
+#            PDL::IO::Pic::rpic("/dev/shm/perl-5.12.1-0.build.tmp/o1iV1Ham33/t byte_a.png") called at t/pic_16bit.t line 51
+#    # Looks like your test exited with 255 just after 2.
+#    t/pic_16bit.t ...................
+#
+# disable tests
+#
+MAKEFLAGS= cpan -f PDL
 cpan PPITerm::UI
 PERL5LIB=".${PERL5LIB:+:$PERL5LIB}" cpan PPI::Document   # required by PPIx::Regexp
 PERL5LIB=".${PERL5LIB:+:$PERL5LIB}" cpan Task::Weaken    # required by PPIx::Regexp