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

third_party/mesa/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 config("mesa_headers_config") {
   include_dirs = [ "src/include" ]
@@ skipping 41 matching lines @@
     "HAVE_LIBEXPAT=1",
     "HAVE_LIBXCB_DRI2=1",
     "FEATURE_GL=1",
     "MAPI_MODE_GLAPI",
 
     #"USE_X86_64_ASM",
     "IN_DRI_DRIVER",
     "USE_XCB",
     "GLX_INDIRECT_RENDERING",
     "GLX_DIRECT_RENDERING",
-    "USE_EXTERNAL_DXTN_LIB=1",
     "IN_DRI_DRIVER",
     "HAVE_ALIAS",
     "HAVE_MINCORE",
     "HAVE_LIBUDEV",
     "_GLAPI_NO_EXPORTS",
   ]
   include_dirs = [
     "src/src/gallium/auxiliary",
     "src/src/gallium/include",
     "src/src/glsl",
@@ skipping 34 matching lines @@
     ]
 
     if (!is_android) {
       defines += [ "HAVE_POSIX_MEMALIGN" ]
     }
 
     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" ]
+  }
 }
 
 # mesa_internal_config is prepended to the config lists.  Flags that
 # disable warnings need to be appended instead so that they show up
 # after flags like -Wall. (gn orders flags on a target before flags from
 # configs.)
 config("mesa_internal_warnings") {
   cflags = []
   if (is_clang) {
     cflags += [
@@ skipping 656 matching lines @@
     deps = [
       "//third_party/wayland:wayland_util",
     ]
 
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [ "//build/config/compiler:no_chromium_code" ]
 
     public_configs = [ ":wayland_drm_protocol_config" ]
   }
 }