Revert "Build system: workaround for compilation under MSYS2"

This reverts commit 016c402a.

The problem has been fixed in MSYS2, see:
https://github.com/msys2/MINGW-packages/pull/8259

configure.ac

@@ -47,20 +47,6 @@ case ${host_os} in
     ;;
 esac
 
-# Workaround for compilation under MSYS2.
-# There is (on 2021-03-29) a problem in the -static-libgfortran linker option that
-# affects the Dynare++ binaries.
-# See https://github.com/msys2/MINGW-packages/issues/7023
-# and https://github.com/msys2/MINGW-packages/issues/6986
-# Until this is fixed, the workaround is to add the --default-image-base-low linker
-# option.
-# We do *not* want to do this when cross-compiling from Debian (because the option does
-# not exist there), hence we test for cross-compilation before applying the workaround.
-AC_CANONICAL_BUILD
-if test "${host_os}" = mingw32 && test "${host_os}" = "${build_os}"; then
-    AM_LDFLAGS="$AM_LDFLAGS -Wl,--default-image-base-low"
-fi
-
 # Use C++ for testing headers
 AC_LANG([C++])