[BUG] better to ban variable length arrays

[yamt]

Description / Steps to reproduce the issue

it seems that we use variable length array (VLA) here and there.
eg.

nuttx/net/usrsock/usrsock_sendmsg.c

Line 145 in 118f827

struct iovec bufs[2 + msg->msg_iovlen];

VLA is a C99 feature and should not be used in the common part of the OS. i guess it's better to add -Wvla there.

On which OS does this issue occur?

[OS: Mac]

What is the version of your OS?

macOS 15.2

NuttX Version

master

Issue Architecture

[Arch: all]

Issue Area

[Area: Other]

Verification

• I have verified before submitting the report.

[yamt]

another example of VLA:

nuttx/libs/libc/stdio/lib_libvsprintf.c

Line 1348 in 118f827

union arg_u argvalue[MAX(numargs, 1)];

[yamt]

nuttx/mm/tlsf/mm_tlsf.c

Line 1051 in 118f827

size_t poolsize[MEMPOOL_NPOOLS];

note: MEMPOOL_NPOOLS is defined using sizeof()