bug#79100: segfault with thread initialization

[a aa]

# version
3.0.10

# `config.guess`
x86_64-pc-linux-gnu

# `config.status`
`--prefix=/usr --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--mandir=/usr/share/man --infodir=/usr/share/info --datadir=/usr/share
--sysconfdir=/etc --localstatedir=/var/lib --datarootdir=/usr/share
--disable-dependency-tracking --disable-silent-rules --disable-static
--docdir=/usr/share/doc/guile-3.0.10-r103
--htmldir=/usr/share/doc/guile-3.0.10-r103/html --with-sysroot=/
--libdir=/usr/lib64 --program-suffix=-3.0
--infodir=/usr/share/guile-data/3.0/info
--with-pkgconfigdir=/usr/share/guile-data/3.0/pkgconfig
--disable-error-on-warning --disable-rpath --disable-lto --enable-posix
--without-libgmp-prefix --without-libiconv-prefix --without-libintl-prefix
--without-libreadline-prefix --without-libunistring-prefix
--disable-guile-debug --disable-debug-malloc --enable-deprecated
--enable-jit --enable-networking --disable-nls --enable-regex
--with-threads build_alias=x86_64-pc-linux-gnu
host_alias=x86_64-pc-linux-gnu CC=gcc 'CFLAGS=-O2 -march=native -pipe
-std=gnu17' LDFLAGS=-fuse-ld=mold
PKG_CONFIG_PATH=/usr/share/guile-data/3.0/pkgconfig`

# How to reproduce
```c
#include <libguile.h>
#include <pthread.h>

void* foo(void*) {
    return NULL;
}

void* run_with_guile(void*)
{
    scm_with_guile(foo, NULL);
    return NULL;
}

int main(void)
{
    pthread_t thread_1, thread_2;
    pthread_create(&thread_1, NULL, run_with_guile, NULL);
    pthread_create(&thread_2, NULL, run_with_guile, NULL);

    pthread_join(thread_1, NULL);
    pthread_join(thread_2, NULL);
    return 0;
}
```

## Output
```txt
Segmentation fault
```

# Intended behaviour
According to the [documentation](
https://www.gnu.org/software/guile/manual/html_node/Guile-Initialization-Functions.html),
you should be able to call `scm_with_guile` concurrently.