Index: lldb/cmake/modules/LLDBConfig.cmake
===================================================================
--- lldb/cmake/modules/LLDBConfig.cmake
+++ lldb/cmake/modules/LLDBConfig.cmake
@@ -250,6 +250,31 @@
   endif()
 endif()
 
+
+# If this is building against a prebuilt Clang, then the Clang resource
+# directory that LLDB is using for its embedded Clang instance needs to point
+# to the resource directory of the used Clang installation.
+if (NOT TARGET clang-resource-headers)
+  if(Clang_DIR)
+    set(LLDB_EXTERNAL_CLANG_RESOURCE_DIR ${Clang_DIR}/../..)
+  elseif(LLVM_DIR)
+    set(LLDB_EXTERNAL_CLANG_RESOURCE_DIR ${LLVM_DIR}/../..)
+  elseif(LLVM_LIBRARY_DIRS)
+    set(LLDB_EXTERNAL_CLANG_RESOURCE_DIR ${LLVM_LIBRARY_DIRS})
+  elseif(LLVM_BUILD_LIBRARY_DIR)
+    set(LLDB_EXTERNAL_CLANG_RESOURCE_DIR ${LLVM_BUILD_LIBRARY_DIR})
+  elseif(LLVM_BINARY_DIR)
+    set(LLDB_EXTERNAL_CLANG_RESOURCE_DIR ${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX})
+  endif()
+  set(clang_version ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH})
+  # Build the final resource directory path by appending 'clang/<version number>'.
+  set(LLDB_EXTERNAL_CLANG_RESOURCE_DIR ${LLDB_EXTERNAL_CLANG_RESOURCE_DIR}/clang/${clang_version})
+  if(NOT EXISTS ${LLDB_EXTERNAL_CLANG_RESOURCE_DIR})
+    unset(LLDB_EXTERNAL_CLANG_RESOURCE_DIR)
+    message(WARNING "Expected directory for clang-resource headers not found: ${LLDB_EXTERNAL_CLANG_RESOURCE_DIR}")
+  endif()
+endif()
+
 # Find Apple-specific libraries or frameworks that may be needed.
 if (APPLE)
   if(NOT APPLE_EMBEDDED)
Index: lldb/cmake/modules/LLDBFramework.cmake
===================================================================
--- lldb/cmake/modules/LLDBFramework.cmake
+++ lldb/cmake/modules/LLDBFramework.cmake
@@ -110,20 +110,7 @@
     add_dependencies(liblldb clang-resource-headers)
     set(clang_resource_headers_dir $<TARGET_PROPERTY:clang-resource-headers,RUNTIME_OUTPUT_DIRECTORY>)
   else()
-    # In standalone builds try the best possible guess
-    if(Clang_DIR)
-      set(clang_lib_dir ${Clang_DIR}/../..)
-    elseif(LLVM_DIR)
-      set(clang_lib_dir ${LLVM_DIR}/../..)
-    elseif(LLVM_LIBRARY_DIRS)
-      set(clang_lib_dir ${LLVM_LIBRARY_DIRS})
-    elseif(LLVM_BUILD_LIBRARY_DIR)
-      set(clang_lib_dir ${LLVM_BUILD_LIBRARY_DIR})
-    elseif(LLVM_BINARY_DIR)
-      set(clang_lib_dir ${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX})
-    endif()
-    set(clang_version ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH})
-    set(clang_resource_headers_dir ${clang_lib_dir}/clang/${clang_version}/include)
+    set(clang_resource_headers_dir ${LLDB_EXTERNAL_CLANG_RESOURCE_DIR}/include)
     if(NOT EXISTS ${clang_resource_headers_dir})
       message(WARNING "Expected directory for clang-resource headers not found: ${clang_resource_headers_dir}")
     endif()
Index: lldb/include/lldb/Host/Config.h.cmake
===================================================================
--- lldb/include/lldb/Host/Config.h.cmake
+++ lldb/include/lldb/Host/Config.h.cmake
@@ -54,4 +54,8 @@
 
 #define LLDB_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}"
 
+// The full path to the resource directory of the Clang that LLDB was build
+// against (or an empty path if LLDB and Clang are build together).
+#define LLDB_EXTERNAL_CLANG_RESOURCE_DIR "${LLDB_EXTERNAL_CLANG_RESOURCE_DIR}"
+
 #endif // #ifndef LLDB_HOST_CONFIG_H
Index: lldb/source/Plugins/ExpressionParser/Clang/ClangHost.cpp
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/ClangHost.cpp
+++ lldb/source/Plugins/ExpressionParser/Clang/ClangHost.cpp
@@ -61,11 +61,22 @@
       "lib" LLDB_LIBDIR_SUFFIX "/lldb/clang",
   };
 
+  std::vector<llvm::SmallString<256>> directories_to_check;
   for (const auto &Suffix : kResourceDirSuffixes) {
     llvm::SmallString<256> clang_dir(parent_dir);
     llvm::SmallString<32> relative_path(Suffix);
     llvm::sys::path::native(relative_path);
     llvm::sys::path::append(clang_dir, relative_path);
+    directories_to_check.push_back(clang_dir);
+  }
+
+  // Check the resource directory if LLDB was build against an existing Clang.
+  // The path is empty if Clang is build alongside LLDB.
+  llvm::SmallString<256> external_clang_dir(LLDB_EXTERNAL_CLANG_RESOURCE_DIR);
+  if (!external_clang_dir.empty())
+    directories_to_check.push_back(external_clang_dir);
+
+  for (const auto &clang_dir : directories_to_check) {
     if (!verify || VerifyClangPath(clang_dir)) {
       LLDB_LOG(log,
                "DefaultComputeClangResourceDir: Setting ClangResourceDir "