using TMPDIR environment variable 's value as TMPDIR macro's value is safe?

[leleliu008]

# Check for temporary directory
AC_MSG_CHECKING(directory to use for temporary files)
if test -n "$enable_tmpdir"; then
    tmpdir="$enable_tmpdir"
elif test -n "$TMPDIR"; then
    tmpdir="$TMPDIR"
elif test -n "$TMP"; then
    tmpdir="$TMP"
elif test -n "$TEMP"; then
    tmpdir="$TEMP"
elif test -d "c:/"; then
    tmpdir="c:/"
else
    tmpdir="/tmp"
fi

If users build uctags from source and do not distribute it to other machines, this is no problem, but if some people distribute it to other machines, I'm not sure if will encounter problem. TMPDIR has been set on macOS and different machine may have different value. If it does exist, what will happen?

[masatake]

See tempFileFP in main/routines.c.
The function needs to be simplified like:

extern FILE *tempFileFP (const char *const mode, char **const pName)
{
	char *name;
	int fd;
#if defined(HAVE_MKSTEMP)
	tempFileFPViaMkstemp();
#elif defined(HAVE_TEMPNAM)
	tempFileFPViaTempnam();
#else
	tempFileFPViaTmpnam();
#endif

	if (fd == -1)
		error (FATAL | PERROR, "cannot open temporary file: %s", name);

	FILE *fp = fdopen (fd, mode);
	if (fp == NULL)
		error (FATAL | PERROR, "cannot open temporary file");
	Assert (*pName == NULL);
	*pName = name;
	return fp;
}

[masatake]

I'll make a pull request just for the transforming.