Can't build VCMI project because of some locking problem in emscripten ports. (assert 'EM_CACHE_IS_LOCKED')

Hi, I found a minor problem that prevents me from building the project (VCMI). When I try to do so, I encounter a locking error while building ports. However, if I use embuild to build the ports, I can successfully build the project.

**Version of emscripten/emsdk:**
* emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.0 (97c7c2adab1791b9487d1f376934a3bdc28f8a67)
* 3.1.68

**OS:** Ubuntu 24.04.1 LTS x64

How to reproduce
```
git clone https://github.com/caiiiycuk/vcmi-wasm.git
cd vcmi-wasm
git checkout vcmi-wasm-1.6.3
git submodule init
git submodule update

mkdir emscripten
cd emscripten

source ~/sdk/emsdk/emsdk_env.sh
emcmake cmake -GNinja -DCMAKE_BUILD_TYPE=MinSizeRel ..
emcc --clear-ports
ninja boost-lib tbb-lib vcmi-extras
ninja -j32 html5 // error here
```

error:
```
caiiiycuk@caiiiycuk-linux:~/vcmi/vcmi-html5/emscripten-2$ ninja -j1 html5
[1/706] cd /home/caiiiycuk/vcmi/vcmi-html5/emscripten-2 && /usr/bin/cmake -DGIT_SHA1="" -P /home/caiiiycuk/vcmi/vcmi-html5/cmake_modules/Version.cmake
-- -- -- Start of Git information
-- GIT_SHA1: e5d305c9ec94b9b05dcae3f97a9d8ef315b1a30c
-- -- -- End of Git information
[2/706] Building CXX object AI/FuzzyLite/fuzzylite/CMakeFiles/fl-obj.dir/src/Benchmark.cpp.o
FAILED: AI/FuzzyLite/fuzzylite/CMakeFiles/fl-obj.dir/src/Benchmark.cpp.o
/home/caiiiycuk/sdk/emsdk/upstream/emscripten/em++ -DDISABLE_VIDEO -DFL_BACKTRACE -DFL_BUILD_PATH=\"/home/caiiiycuk/vcmi/vcmi-html5\" -DM_BIN_DIR=\".\" -DM_DATA_DIR=\".\" -DM_LIB_DIR=\".\" -DVCMI_HTML5_BUILD -DVCMI_NO_THREADED_LOAD -DVCMI_VERSION_MAJOR=1 -DVCMI_VERSION_MINOR=7 -DVCMI_VERSION_PATCH=0 -DVCMI_VERSION_STRING=\"1.7.0\" -I/home/caiiiycuk/vcmi/vcmi-html5/emscripten-2/boost/include -I/home/caiiiycuk/vcmi/vcmi-html5/emscripten-2/tbb/include -I/home/caiiiycuk/vcmi/vcmi-html5/AI/FuzzyLite/fuzzylite -I/home/caiiiycuk/vcmi/vcmi-html5/include -I/home/caiiiycuk/vcmi/vcmi-html5/lib -I/home/caiiiycuk/vcmi/vcmi-html5 -I/home/caiiiycuk/vcmi/vcmi-html5/AI/FuzzyLite/fuzzylite/. -pedantic -Wall -Wextra -Wall -Wextra -Wpointer-arith -Wuninitialized -Wmismatched-tags -Wno-unused-parameter -Wno-switch -Wno-reorder -Wno-sign-compare -Wno-varargs -Wno-non-literal-null-conversion -Wno-varargs -Os -DNDEBUG -std=gnu++17 -std=c++11 -fPIC -sUSE_SDL=2 -sUSE_SDL_IMAGE=2 -sUSE_SDL_MIXER=2 -sUSE_SDL_TTF=2 -sUSE_ZLIB=1 -pthread -fwasm-exceptions -Oz -fcolor-diagnostics -Wno-error=deprecated-declarations -MD -MT AI/FuzzyLite/fuzzylite/CMakeFiles/fl-obj.dir/src/Benchmark.cpp.o -MF AI/FuzzyLite/fuzzylite/CMakeFiles/fl-obj.dir/src/Benchmark.cpp.o.d -o AI/FuzzyLite/fuzzylite/CMakeFiles/fl-obj.dir/src/Benchmark.cpp.o -c /home/caiiiycuk/vcmi/vcmi-html5/AI/FuzzyLite/fuzzylite/src/Benchmark.cpp
cache:INFO: generating port: sysroot/lib/wasm32-emscripten/libSDL2_ttf-mt.a... (this will be cached in "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/libSDL2_ttf-mt.a" for subsequent builds)
Traceback (most recent call last):
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/emcc.py", line 1660, in
sys.exit(main(sys.argv))
^^^^^^^^^^^^^^
File "/usr/lib/python3.12/contextlib.py", line 81, in inner
return func(*args, **kwds)
^^^^^^^^^^^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/emcc.py", line 1653, in main
ret = run(args)
^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/emcc.py", line 670, in run
linker_inputs = phase_compile_inputs(options, state, newargs, input_files)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/contextlib.py", line 81, in inner
return func(*args, **kwds)
^^^^^^^^^^^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/emcc.py", line 1031, in phase_compile_inputs
cmd = get_clang_command() + inputs
^^^^^^^^^^^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/emcc.py", line 992, in get_clang_command
return compiler + get_cflags(state.orig_args, use_cxx) + compile_args
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/emcc.py", line 459, in get_cflags
ports.add_cflags(cflags, settings)
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/tools/ports/__init__.py", line 577, in add_cflags
port.get(Ports, settings, shared)
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/tools/ports/freetype.py", line 101, in get
return [shared.cache.get_lib(get_lib_name(settings), create, what='port')]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/tools/cache.py", line 150, in get_lib
return get(name, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/tools/cache.py", line 168, in get
with lock(shortname):
File "/usr/lib/python3.12/contextlib.py", line 137, in __enter__
return next(self.gen)
^^^^^^^^^^^^^^
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/tools/cache.py", line 68, in lock
acquire_cache_lock(reason)
File "/home/caiiiycuk/sdk/emsdk/upstream/emscripten/tools/cache.py", line 42, in acquire_cache_lock
assert 'EM_CACHE_IS_LOCKED' not in os.environ, f'attempt to lock the cache while a parent process is holding the lock ({reason})'
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: attempt to lock the cache while a parent process is holding the lock (sysroot/lib/wasm32-emscripten/libfreetype.a)
em++: error: subprocess 1/1 failed (returned 1)! (cmdline: /home/caiiiycuk/sdk/emsdk/upstream/emscripten/emcc -c /home/caiiiycuk/sdk/emsdk/upstream/emscripten/cache/ports/sdl2_ttf/SDL_ttf-release-2.20.2/SDL_ttf.c -o /home/caiiiycuk/sdk/emsdk/upstream/emscripten/cache/ports-builds/sdl2_ttf/SDL_ttf.c.o -g -sSTRICT -Werror -O2 -I/home/caiiiycuk/sdk/emsdk/upstream/emscripten/cache/ports/sdl2_ttf/SDL_ttf-release-2.20.2 -DTTF_USE_HARFBUZZ=1 -sUSE_SDL=2 -sUSE_FREETYPE -sUSE_HARFBUZZ -pthread)
ninja: build stopped: subcommand failed.
caiiiycuk@caiiiycuk-linux:~/vcmi/vcmi-html5
```

Related to [vcmi#5291](https://github.com/vcmi/vcmi/pull/5291)