Fixes https://github.com/microsoft/mimalloc/issues/1158.

[emeryberger]

One-liner, adds libraries to link step for stress test. Verified that this fixes #1158. Also tested on Mac and Amazon Linux 2023.

Before:

[ 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

After:

[ 95%] Linking C executable mimalloc-test-stress
[ 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
[100%] Built target mimalloc-test-stress-dynamic