Don't check for C++11 features if C++11 support is disabled

CMakeLists.txt

@@ -43,7 +43,7 @@ set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH}
   "${CMAKE_CURRENT_SOURCE_DIR}/support/cmake")
 
-include(testCxx11)
+include(cxx11)
 
 if (CMAKE_COMPILER_IS_GNUCXX OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang"))
   set(PEDANTIC_COMPILE_FLAGS -Wall -Wextra -Wshadow -pedantic)

support/cmake/cxx11.cmake

@@ -1,3 +1,9 @@
+# C++11 feature support detection
+
+if (NOT FMT_USE_CPP11)
+  return()
+endif ()
+
 include(CheckCXXCompilerFlag)
 
 if (FMT_USE_CPP11)

test/CMakeLists.txt

@@ -40,6 +40,8 @@ target_compile_definitions(test-main PUBLIC
   FMT_USE_FILE_DESCRIPTORS=$<BOOL:${HAVE_OPEN}>)
 target_link_libraries(test-main gmock cppformat)
 
+include(CheckCXXCompilerFlag)
+
 # Workaround GTest bug https://github.com/google/googletest/issues/705.
 check_cxx_compiler_flag(
   -fno-delete-null-pointer-checks HAVE_FNO_DELETE_NULL_POINTER_CHECKS)