Bug 166349

In POSIX.1-2008, the %c , %s , and %[ conversion specifiers in a
fscanf()/scanf()/sscanf() format string accept an optional
assignment-allocation character 'm' to allocate a memory buffer large enough
to hold the converted string:

http://pubs.opengroup.org/onlinepubs/9699919799/functions/fscanf.html

This functionality is useful for safely reading formatted input strings of unknown size.

The FreeBSD 9.0 libc does not support this feature.

In addition, the gcc 4.6.3 port silently accepts the assignment-allocation character, even when "-Wall" is specified, but a memory buffer is apparently not allocated at run time.

Fix: Patch attached with submission follows:
How-To-Repeat: Compile the attached program (scanf_m.c) using the base gcc 4.2.1:

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$ gcc -Wall scanf_m.c
scanf_m.c: In function 'main':
scanf_m.c:6: warning: unknown conversion type character 'm' in format
scanf_m.c:6: warning: too many arguments for format
$ echo test | ./a.out
H??
Segmentation fault (core dumped)
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Using the gcc 4.6.3 port:
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$ gcc46 -Wall scanf_m.c
$ echo test | ./a.out
H??
Segmentation fault (core dumped)
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