fix(unittests): coredump when running unit tests #18663

fs_init() must be called before early_init() in init/helpers.lua

If I run 'make unittest' on my Mac (macOS 10.14/Mojave or 12/Big Sur, intel
CPU), every test produce a core dump.

Call sequence in the core is:
    early_init()            main.c:197
    set_init_1()            option.c:508
    runtimepath_default()   runtime.c:1205
    get_lib_dir()           runtime.c:1175
    os_isdir()              fs.c:137
    os_getperm()            fs.c:777
    os_stat()               fs.c:761
    fs_loop_lock()          fs.c:72
    uv_mutex_lock(&fs_loop_mutex)   thread.c:352
    abort()

.deps/build/src/libuv/src/unix/thread.c:

    void uv_mutex_lock(uv_mutex_t* mutex) {
      if (pthread_mutex_lock(mutex))
        abort();	// line 352
    }

So pthread_mutex_lock(&fs_loop_mutex) failed. The reason seems to be simple.
fs_init() was not called and fs_loop_mutex has not been initialized. fs_init()
was moved out from early_init() in main.c by
b87867e69e94d9784468a126f21c721446f080de, but unit/helpers.lua was not updated
accordingly.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/nvim/os/fs.h b/src/nvim/os/fs.h
new file mode 100644
index 0000000000..b03090dfee
--- /dev/null
+++ b/src/nvim/os/fs.h
@@ -0,0 +1,7 @@
+#ifndef NVIM_OS_FS_H
+#define NVIM_OS_FS_H
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "os/fs.h.generated.h"
+#endif
+#endif  // NVIM_OS_FS_H