Add a m-spectest5_precompile to run tests in precompilation mode

Currently this fails for both tests that use 'use lib' or have
precompilation only bugs. Fixing the 'use lib' part need further
work.

t/harness5

@@ -28,6 +28,7 @@ GetOptions(
     'quick:1'           => \my $do_quick,
     'stress:1'          => \my $do_stress,
     'archive=s'         => \my $archive,
+    'precompile'        => \my $precompile,
     'jvm'               => \my $jvm,
     'js'               => \my $js,
     'moar'              => \my $moar,
@@ -120,8 +121,9 @@ if ($jvm) {
 }
 
 if (eval "require $tap_harness_class;") {
+    my $run_with_perl = $precompile ? [$ENV{HARNESS_PERL}, 't/precompileandrun'] : [$ENV{HARNESS_PERL}];
     my %harness_options = (
-        exec        => $jvm ? [$^X, "./eval-client.pl", "TESTTOKEN", "run"] : [$ENV{HARNESS_PERL}],
+        exec        => $jvm ? [$^X, "./eval-client.pl", "TESTTOKEN", "run"] : $run_with_perl,
         verbosity   => 0+$Test::Harness::verbose,
         jobs        => $jobs,
         ignore_exit => 1,
@@ -239,6 +241,7 @@ Options:
     --slow - spread tests marked "slow" equally over the run (default on non-Win)
     --moar/--jvm/--js - mutually exclusive. Use MoarVM/JVM backend
     --no-merge - pass STDERR from the tests through to the terminal's STDERR
+    --precompile - precompile tests before running them
 
     --verbosity=[level] - set the verbosity level.
        1   verbose        Print individual test results to STDOUT.

t/precompileandrun

@@ -0,0 +1,2 @@
+$*REPO.precomp-repository.precompile(@*ARGS[0].IO, 'precompiled_test', :force);
+$*REPO.precomp-repository.load('precompiled_test');

tools/build/Makefile-Moar.in

@@ -240,6 +240,10 @@ m-coretest5: m-all
 m-spectest5: m-testable t/spectest.data
 	$(M_HARNESS5_WITH_FUDGE) --tests-from-file=t/spectest.data
 
+# Run the spectests that we know work after precompiling them.
+m-spectest5_precompile: m-testable t/spectest.data
+	$(M_HARNESS5_WITH_FUDGE) --precompile --tests-from-file=t/spectest.data
+
 m-spectest_full5: m-testable
 	$(M_HARNESS5_WITH_FUDGE) t/spec