mesa: Disable support for loading libtxc_dxtn.so if msan is enabled.

third_party/mesa/BUILD.gn

Index: third_party/mesa/BUILD.gn
diff --git a/third_party/mesa/BUILD.gn b/third_party/mesa/BUILD.gn
index d4b1f99230975ece4d66919fcc78439f41c009ef..26eef9744fc91c33d97c404404dcfdacebd11e71 100644
--- a/third_party/mesa/BUILD.gn
+++ b/third_party/mesa/BUILD.gn
@@ -59,7 +59,6 @@ config("mesa_internal_config") {
     "USE_XCB",
     "GLX_INDIRECT_RENDERING",
     "GLX_DIRECT_RENDERING",
-    "USE_EXTERNAL_DXTN_LIB=1",
     "IN_DRI_DRIVER",
     "HAVE_ALIAS",
     "HAVE_MINCORE",
@@ -114,6 +113,10 @@ config("mesa_internal_config") {
       cflags += [ "-fPIC" ]
     }
   }
+
+  if (is_msan) {
+    defines += [ "USE_EXTERNAL_DXTN_LIB=0" ]

[Nico, 2017/05/11 15:05:33]

Add comment for as to why. Also, we could probably just add this to the prebuilt
libs so that msan tests what we actually ship. (But I think the plan is for us
to no longer depend on mesa eventually. Then again, those plans sometimes take a
long time to materialize and might change in the future.)

+  }
 }
 
 # mesa_internal_config is prepended to the config lists.  Flags that