Makefile: Fix multiple custom command outputs regression (#15116)

In commit v3.2.0-rc1~272^2~2 (Makefile: Fix rebuild with multiple custom
command outputs, 2014-12-05) we changed the generated makefile pattern
for multiple outputs from

  out1: depends...
          commands...
  out2: out1

to

  out1 out2: depends...
          commands...

This was based on the incorrect assumption that make tools would treat
this as a combined output rule and run the command(s) exactly once for
them.  It turns out that instead this new pattern is equivalent to

  out1: depends...
          commands...
  out2: depends...
          commands...

so the commands may be run more than once.

Some documents suggest using a "dedicated witness" stamp file:

  stamp: depends...
          rm -f stamp
          touch stamp.tmp
          commands...
          mv stamp.tmp stamp
  out1 out2: stamp

However, if the commands fail the error message will refer to the stamp
instead of any of the real outputs, which may be confusing to readers.
Also, this approach seems to have the same behavior of the original
approach that motiviated the above commit: multiple invocations are
needed to bring consumers of the outputs up to date.

Instead we can return to the original approach but add an explicit
touch to each extra output rule:

  out1: depends...
          commands...
  out2: out1
          touch -c out2

This causes make tools to recognize that all outputs have changed and
therefore to execute any commands that consume them.

1 files changed, 2 insertions, 3 deletions

diff --git a/Source/cmMakefileLibraryTargetGenerator.cxx b/Source/cmMakefileLibraryTargetGenerator.cxx
index cdda36c52c..e55f6512e5 100644
--- a/Source/cmMakefileLibraryTargetGenerator.cxx
+++ b/Source/cmMakefileLibraryTargetGenerator.cxx
@@ -765,9 +765,8 @@ void cmMakefileLibraryTargetGenerator::WriteLibraryRules
     }
 
   // Write the build rule.
-  this->LocalGenerator->WriteMakeRule(*this->BuildFileStream, 0,
-                                      outputs, depends, commands, false);
-
+  this->WriteMakeRule(*this->BuildFileStream, 0, outputs,
+                      depends, commands, false);
 
   // Write the main driver rule to build everything in this target.
   this->WriteTargetDriverRule(targetFullPath, relink);