Revert of 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 03c52a397390c304905f2bc8618aef6a0ec39bf8..d4b1f99230975ece4d66919fcc78439f41c009ef 100644
--- a/third_party/mesa/BUILD.gn
+++ b/third_party/mesa/BUILD.gn
@@ -59,6 +59,7 @@
     "USE_XCB",
     "GLX_INDIRECT_RENDERING",
     "GLX_DIRECT_RENDERING",
+    "USE_EXTERNAL_DXTN_LIB=1",
     "IN_DRI_DRIVER",
     "HAVE_ALIAS",
     "HAVE_MINCORE",
@@ -112,14 +113,6 @@
     if (!is_android && !is_mac) {
       cflags += [ "-fPIC" ]
     }
-  }
-
-  if (is_msan) {
-    # Disable code in mesa that loads the libtxc_dxtn.so library if msan is
-    # enabled, as the library will be loaded from a system directory, which
-    # may cause spurious msan reports because msan expects most libraries in
-    # the process to be compiled with msan.
-    defines += [ "USE_EXTERNAL_DXTN_LIB=0" ]
   }
 }