build: make --enable-werror just -Werror

No longer special case a set of warnings, to make up our own -Werror,
just use -Werror outright. This shouldn't really have any effect on
existing builders, who were already using --enable-werror, and is more
inline with what they would expect --enable-werror to be, which is
erroring on any/all warnings.

We keep -Wno-error=return-type because we know that is broken when using
mingw-w64. It should only be applied when cross-compiling for Windows.

Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

configure.ac

@@ -315,7 +315,7 @@ AC_ARG_ENABLE([gprof],
 dnl Turn warnings into errors
 AC_ARG_ENABLE([werror],
     [AS_HELP_STRING([--enable-werror],
-                    [Treat certain compiler warnings as errors (default is no)])],
+                    [Treat compiler warnings as errors (default is no)])],
     [enable_werror=$enableval],
     [enable_werror=no])
 
@@ -403,34 +403,13 @@ if test "x$enable_werror" = "xyes"; then
   if test "x$CXXFLAG_WERROR" = "x"; then
     AC_MSG_ERROR("enable-werror set but -Werror is not usable")
   fi
-  AX_CHECK_COMPILE_FLAG([-Werror=gnu],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=gnu"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=vla],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=vla"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=shadow-field],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=shadow-field"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=switch],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=switch"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=thread-safety],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=thread-safety"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=range-loop-analysis],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=range-loop-analysis"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=unused-variable],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=unused-variable"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=date-time],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=date-time"],,[[$CXXFLAG_WERROR]])
+  ERROR_CXXFLAGS=$CXXFLAG_WERROR
 
   dnl -Wreturn-type is broken in GCC for MinGW-w64.
   dnl https://sourceforge.net/p/mingw-w64/bugs/306/
-  AX_CHECK_COMPILE_FLAG([-Werror=return-type], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=return-type"], [], [$CXXFLAG_WERROR],
+  AX_CHECK_COMPILE_FLAG([-Werror=return-type], [], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Wno-error=return-type"], [$CXXFLAG_WERROR],
                         [AC_LANG_SOURCE([[#include <cassert>
                                           int f(){ assert(false); }]])])
-
-  AX_CHECK_COMPILE_FLAG([-Werror=conditional-uninitialized],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=conditional-uninitialized"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=sign-compare],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=sign-compare"],,[[$CXXFLAG_WERROR]])
-  dnl -Wsuggest-override is broken with GCC before 9.2
-  dnl https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78010
-  AX_CHECK_COMPILE_FLAG([-Werror=suggest-override],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=suggest-override"],,[[$CXXFLAG_WERROR]],
-                        [AC_LANG_SOURCE([[struct A { virtual void f(); }; struct B : A { void f() final; };]])])
-  AX_CHECK_COMPILE_FLAG([-Werror=unreachable-code-loop-increment],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=unreachable-code-loop-increment"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Werror=mismatched-tags], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=mismatched-tags"], [], [$CXXFLAG_WERROR])
-  AX_CHECK_COMPILE_FLAG([-Werror=implicit-fallthrough], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=implicit-fallthrough"], [], [$CXXFLAG_WERROR])
-
-  if test x$suppress_external_warnings != xno ; then
-    AX_CHECK_COMPILE_FLAG([-Werror=documentation],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=documentation"],,[[$CXXFLAG_WERROR]])
-  fi
 fi
 
 if test "x$CXXFLAGS_overridden" = "xno"; then
@@ -454,6 +433,8 @@ if test "x$CXXFLAGS_overridden" = "xno"; then
   AX_CHECK_COMPILE_FLAG([-Wduplicated-cond],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wduplicated-cond"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wlogical-op],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wlogical-op"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Woverloaded-virtual],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Woverloaded-virtual"],,[[$CXXFLAG_WERROR]])
+  dnl -Wsuggest-override is broken with GCC before 9.2
+  dnl https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78010
   AX_CHECK_COMPILE_FLAG([-Wsuggest-override],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wsuggest-override"],,[[$CXXFLAG_WERROR]],
                         [AC_LANG_SOURCE([[struct A { virtual void f(); }; struct B : A { void f() final; };]])])
   AX_CHECK_COMPILE_FLAG([-Wunreachable-code-loop-increment],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wunreachable-code-loop-increment"],,[[$CXXFLAG_WERROR]])