Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -186,7 +186,9 @@
 
 # Don't look for libxml if we're using MSan, since uninstrumented third party
 # code may call MSan interceptors like strlen, leading to false positives.
-if(NOT LLVM_USE_SANITIZER MATCHES "Memory.*")
+# Similarly, don't look for libxml on the host if we have a specific sysroot or
+# are cross-compiling.
+if(NOT CMAKE_SYSROOT AND NOT CMAKE_CROSSCOMPILING AND NOT LLVM_USE_SANITIZER MATCHES "Memory.*")
   set (LIBXML2_FOUND 0)
   find_package(LibXml2 2.5.3 QUIET)
   if (LIBXML2_FOUND)