CMake: Disable -Wundefined-var-template for clang

This warning leads to a lot of false positives. Simply disable the
diagnostic.

Fixes #3705

diff --git a/cmake/setup_compiler_flags_gnu.cmake b/cmake/setup_compiler_flags_gnu.cmake
index eec2173315c02fd7adb2be0462a55c00db94208c..461c8107eea1af31fc721e854462f99ed68a12f8 100644 (file)
--- a/cmake/setup_compiler_flags_gnu.cmake
+++ b/cmake/setup_compiler_flags_gnu.cmake
@@ -110,6 +110,12 @@ IF(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   ENABLE_IF_SUPPORTED(DEAL_II_CXX_FLAGS "-Wno-variadic-macros")
   ENABLE_IF_SUPPORTED(DEAL_II_CXX_FLAGS "-Wno-c++11-extensions")
 
+  #
+  # Disable a diagnostic that warns about potentially uninstantiated static
+  # members. This leads to a ton of false positives.
+  #
+  ENABLE_IF_SUPPORTED(DEAL_II_CXX_FLAGS "-Wno-undefined-var-template")
+
   #
   # Clang versions prior to 3.6 emit a lot of false positives wrt
   # "-Wunused-function". Also suppress warnings for Xcode older than 6.3