Using newlib and common malloc is not thread safe

[talih0]

Describe the bug

Using COMMON_LIBC_MALLOC and NEWLIB_LIBC is not thread safe.
Both implementations share the same heap, but each has their own locking mechanism.

This will cause memory corruptions when malloc() and newlib (i.e. printf()) are used in different threads.

To Reproduce
Steps to reproduce the behavior:

Checkout out my branch where I've modified samples/basic/threads to use printf() and malloc():
https://github.com/talih0/zephyr/tree/malloc_newlib_crash

I could reproduce the crash on two boards: xmc47_relax_kit and sam_v71_xult.
I did not get the crash when using qemu_86.

1. west build -b sam_v71_xult samples/basic/threads
2. west flash
3. picocom -e b -b 115200 /dev/ttyACM0

%%%ѥUzMեrrjj:2*2RRRj
                    Count 1
Count 1
ASSERTION FAIL [chunk_used(h, c)] @ WEST_TOPDIR/zephyr/lib/heap/heap.c:175
        unexpected heap state (double-free?) for memory at 0x71c92764

Expected behavior
No crash.

Environment (please complete the following information):

• OS: Linux
• Toolchain Zephyr SDK 16.5
• Commit SHA or Version used: https://github.com/talih0/zephyr/tree/malloc_newlib_crash