Limit clang-sparc64-linux-multistage to Sparc target.

This helps reducing the build time a little as we are interested in the Sparc target only anyway.

Reviewed By: gkistanova

Differential Revision: https://reviews.llvm.org/D90521
diff --git a/buildbot/osuosl/master/config/builders.py b/buildbot/osuosl/master/config/builders.py
index cf089b4..257392a 100644
--- a/buildbot/osuosl/master/config/builders.py
+++ b/buildbot/osuosl/master/config/builders.py
@@ -655,7 +655,8 @@
                     stage1_config='Release',
                     stage2_config='Release',
                     extra_cmake_args=['-DLLVM_ENABLE_ASSERTIONS=ON',
-                                      '-DLLVM_PARALLEL_LINK_JOBS=4'])},
+                                      '-DLLVM_PARALLEL_LINK_JOBS=4',
+                                      '-DLLVM_TARGETS_TO_BUILD=Sparc'])},
 
     {'name' : "clang-hexagon-elf",
     'tags'  : ["clang"],