All supported versions of Clang and GCC support at least C++17 now

Change-Id: I9130d0d1fceeb6efb1f324c99acd38eb92e67850
Reviewed-on: https://gerrit.libreoffice.org/64733
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

configure.ac

@@ -6205,12 +6205,12 @@ dnl ===================================================================
 dnl C++11
 dnl ===================================================================
 
-AC_MSG_CHECKING([whether $CXX supports C++17, C++14, or C++11])
+AC_MSG_CHECKING([whether $CXX supports C++17])
 CXXFLAGS_CXX11=
 if test "$COM" = MSC -a "$COM_IS_CLANG" != TRUE; then
     CXXFLAGS_CXX11=-std:c++17
 elif test "$GCC" = "yes" -o "$COM_IS_CLANG" = TRUE; then
-    my_flags='-std=gnu++2a -std=c++2a -std=gnu++17 -std=gnu++1z -std=c++17 -std=c++1z -std=gnu++14 -std=gnu++1y -std=c++14 -std=c++1y -std=gnu++11 -std=gnu++0x -std=c++11 -std=c++0x'
+    my_flags='-std=gnu++2a -std=c++2a -std=gnu++17 -std=gnu++1z -std=c++17 -std=c++1z'
     for flag in $my_flags; do
         if test "$COM" = MSC; then
             flag="-Xclang $flag"

external/libcmis/StaticLibrary_libcmis.mk

@@ -13,13 +13,10 @@ $(eval $(call gb_StaticLibrary_set_warnings_not_errors,libcmis))
 
 ifeq ($(COM_IS_CLANG),TRUE)
 # Avoid narrowing conversion error (even though the option is technically a warning)
-# caused by boost.
-# Also avoid -Wdynamic-exception-spec errors in C++17 mode.
+# caused by boost, and avoid -Wdynamic-exception-spec errors.
 $(eval $(call gb_StaticLibrary_add_cxxflags,libcmis,\
     -Wno-error=c++11-narrowing \
-    $(if $(filter -std=gnu++2a -std=c++2a -std=gnu++17 -std=gnu++1z -std=c++17 -std=c++1z, \
-            $(CXXFLAGS_CXX11)), \
-        -Wno-error=dynamic-exception-spec) \
+    -Wno-error=dynamic-exception-spec \
 ))
 endif