gdal: Use C++17 standard for std::optional in poppler

mingw-w64-gdal/PKGBUILD

@@ -8,7 +8,7 @@ _realname=gdal
 pkgbase=mingw-w64-${_realname}
 pkgname="${MINGW_PACKAGE_PREFIX}-${_realname}"
 pkgver=3.3.3
-pkgrel=3
+pkgrel=4
 pkgdesc="A translator library for raster geospatial data formats (mingw-w64)"
 arch=('any')
 mingw_arch=('mingw32' 'mingw64' 'ucrt64' 'clang64' 'clang32')
@@ -88,6 +88,8 @@ build() {
   cd "${srcdir}/build-${MSYSTEM}"
 
   CFLAGS+=" -fno-strict-aliasing"
+  CXXFLAGS+=" -std=c++17 -Wno-deprecated-declarations"
+
   # somehow the configure test for redeclaring sprintf succeeds but
   # then errors during the build with clang.
   CPPFLAGS+=" -DDONT_DEPRECATE_SPRINTF"