Fix a variety of memory management issues

[ghaerr]

Based on issues found when rewriting ELKS sbrk/brk and stack check routines. (To be posted on ELKS shortly).

This PR fixes the following:

• Realloc bug in nasm and nasm32
• Removes buggy alloca in ar86. Now checks for alloca failure for symtab.
• Adds stddef.h header for C86
• Attempts to add standard 4K stack and 16k heap sizes for tools. This turned out a bit tricky, since some tools are almost out of heap space.

Tested toolchain on ELKS using rewritten ELKS libc malloc, all working. (PR coming shortly for malloc fix on ELKS).

[rafael2k]

Thanks @ghaerr. Indeed, with nasm we are tight on memory...

[ghaerr]

Thanks @rafael2k. You'll want to use the enhancements in ghaerr/elks#2128 for your further testing.

You might also notice I added a "make copy" which can be used after a "make" all, this copies libc.a and elks-bin/* to the ELKS rootfs_template/root directory (home directory of /root) for easier QEMU testing of binaries.