final step of build (`mimalloc-test-stress-dynamic`) fails on Amazon Linux 2

Nobody has claimed this yet.

# Bug description

* final step of build (`mimalloc-test-stress-dynamic`) fails on Amazon Linux 2

## Steps to reproduce:

* clone on Amazon Linux 2 instance, try to build as usual (`mkdir build && cd build && cmake .. && make`).

## Other information

```
$ uname -a
Linux xxx.us-east-1.amazon.com xxx.xxx #1 SMP Sat Sep 20 21:53:55 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
```

## Error message (truncated):

```
[ 95%] Built target mimalloc-test-stress
[ 97%] Building C object CMakeFiles/mimalloc-test-stress-dynamic.dir/test/test-stress.c.o
[100%] Linking C executable mimalloc-test-stress-dynamic
CMakeFiles/mimalloc-test-stress-dynamic.dir/test/test-stress.c.o: In function `main':
test-stress.c:(.text.startup+0x106): undefined reference to `pthread_create'
test-stress.c:(.text.startup+0x12c): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
make[2]: *** [mimalloc-test-stress-dynamic] Error 1
make[1]: *** [CMakeFiles/mimalloc-test-stress-dynamic.dir/all] Error 2
make: *** [all] Error 2
```

## Fix status

PR incoming.

Reproduce the failure on Amazon Linux 2 with `mkdir build && cd build && cmake .. && make`. Inspect the CMake configuration for `mimalloc-test-stress-dynamic` and the referenced `test/test-stress.c`; done means the final target links successfully and the complete build finishes.

Written by the indexing model from the issue text.