Documented bugpoint --compile-custom --compile-command.

I've used it a few times to reduce unit tests and gotten one request for information on it. It's not easy to use correctly because bugpoint doesn't tell you when you're doing it wrong.

llvm-svn: 129507

llvm/docs/CommandGuide/bugpoint.pod

@@ -21,7 +21,7 @@ distribution.
 
 =head1 OPTIONS
 
-=over 
+=over
 
 =item B<--additional-so> F<library>
 
@@ -87,7 +87,7 @@ mis-management.
 =item B<-find-bugs>
 
 Continually randomize the specified passes and run them on the test program
-until a bug is found or the user kills B<bugpoint>. 
+until a bug is found or the user kills B<bugpoint>.
 
 =item B<-help>
 
@@ -147,6 +147,20 @@ This option defines the command to use with the B<--run-custom> and
 B<--safe-custom> options to execute the bitcode testcase. This can
 be useful for cross-compilation.
 
+=item B<--compile-command> I<command>
+
+This option defines the command to use with the B<--compile-custom>
+option to compile the bitcode testcase. This can be useful for
+testing compiler output without running any link or execute stages. To
+generate a reduced unit test, you may add CHECK directives to the
+testcase and pass the name of a compile-command script in this form:
+
+    llc "$@"
+    not FileCheck [bugpoint input file].ll < bugpoint-test-program.s
+
+This script will "fail" as long as FileCheck passes. So the result
+will be the minimum bitcode that passes FileCheck.
+
 =item B<--safe-path> I<path>
 
 This option defines the path to the command to execute with the