poppler test depends on to-be-remove C++ feature

```
warning: undefined symbol: FcPatternGetString (referenced by root reference (e.g. compiled C/C++ code))
In file included from poppler-global.cpp:20:
In file included from ./poppler-global.h:37:
In file included from /b/s/w/ir/x/w/install/emscripten/cache/sysroot/include/c++/v1/iosfwd:99:
In file included from /b/s/w/ir/x/w/install/emscripten/cache/sysroot/include/c++/v1/__fwd/fstream.h:13:
/b/s/w/ir/x/w/install/emscripten/cache/sysroot/include/c++/v1/__fwd/string.h:45:41: error: 'char_traits' is deprecated: char_traits for T not equal to char, wchar_t, char8_t, char16_t or char32_t is non-standard and is provided for a temporary period. It will be removed in LLVM 18, so please migrate off of it. [-Werror,-Wdeprecated-declarations]
45 | template , class _Allocator = allocator<_CharT> >
| ^
poppler-global.cpp:205:12: note: in instantiation of default argument for 'basic_string' required here
205 | : std::basic_string(len, ch)
| ^~~~~~~~~~~~~~~~~~~~~~~~
/b/s/w/ir/x/w/install/emscripten/cache/sysroot/include/c++/v1/__string/char_traits.h:79:8: note: 'char_traits' has been explicitly marked deprecated here
79 | struct _LIBCPP_DEPRECATED_("char_traits for T not equal to char, wchar_t, char8_t, char16_t or char32_t is non-standard and is provided for a temporary period. It will be removed in LLVM 18, so please migrate off of it.")
| ^
/b/s/w/ir/x/w/install/emscripten/cache/sysroot/include/c++/v1/__config:958:53: note: expanded from macro '_LIBCPP_DEPRECATED_'
958 | # define _LIBCPP_DEPRECATED_(m) __attribute__((__deprecated__(m)))
| ^
1 error generated.
em++: error: '/b/s/w/ir/x/w/install/bin/clang++ -target wasm32-unknown-emscripten -fignore-exceptions -fvisibility=default -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --sysroot=/b/s/w/ir/x/w/install/emscripten/cache/sysroot -DEMSCRIPTEN -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -DHAVE_CONFIG_H -I. -I.. -I../poppler -I.. -I../goo -I../poppler -Dpoppler_cpp_EXPORTS -Wall -Wno-write-strings -Woverloaded-virtual -Wnon-virtual-dtor -Wcast-align -fno-exceptions -fno-common -Werror -Os -Wno-misleading-indentation -Wno-unused-but-set-variable -Wno-pointer-bool-conversion -Wno-shift-negative-value -Wno-gnu-offsetof-extensions -Wno-unknown-warning-option -I/b/s/w/ir/x/w/install/emscripten/test/third_party/freetype/include -I/b/s/w/ir/x/w/install/emscripten/test/third_party/poppler/include -Wno-sentinel -Wno-logical-not-parentheses -Wno-unused-private-field -Wno-tautological-compare -Wno-unknown-pragmas -Wno-shift-negative-value -Wno-dynamic-class-memaccess -Wno-unused-command-line-argument -ansi -MT libpoppler_cpp_la-poppler-global.lo -MD -MP -MF .deps/libpoppler_cpp_la-poppler-global.Tpo -c poppler-global.cpp -o libpoppler_cpp_la-poppler-global.o' failed (returned 1)
make[3]: *** [Makefile:575: libpoppler_cpp_la-poppler-global.lo] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [Makefile:679: all-recursive] Error 1
make[1]: *** [Makefile:537: all-recursive] Error 1
make: *** [Makefile:418: all] Error 2
cache:INFO: generating system asset: symbol_lists/123c5414ec89c9f43accaf55df6e0ea262d549f5.json... (this will be cached in "/b/s/w/ir/x/w/install/emscripten/cache/symbol_lists/123c5414ec89c9f43accaf55df6e0ea262d549f5.json" for subsequent builds)
```