Avoid using a gcc compiler language extension
Avoid using a gcc compiler language extension

In particular, using pointer arithmetic on void pointers,
despite being quite useful, is not legal in standard C.
Avoiding non-standard C constructs will help in porting
the library to other compilers/platforms.

Signed-off-by: Ramsay Jones <3e74413778ce9c8bebbbaedfd56741f6850faeaf@ramsay1.demon.co.uk>
Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

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