NetBSD emits:
warning: Warning: reference to the libc supplied alloca(3); this most likely will not work. Please use the compiler provided version of alloca(3), by supplying the appropriate compiler flags (e.g. not -std=c89).
and man 3 alloca says:
Normally, gcc(1) translates calls to alloca() with inlined code. This is not done when either the -ansi, -std=c89, -std=c99, or the
-std=c11 option is given and the header <alloca.h> is not included. Otherwise, (without an -ansi or -std=c* option) the glibc version of
<stdlib.h> includes <alloca.h> and that contains the lines:
#ifdef __GNUC__
#define alloca(size) __builtin_alloca (size)
#endif
It looks like alloca is a bad idea in modern C/C++, so we use
VLAs for C and std::vector for C++.
