Fix StaticAnalyzer complaints. NFC.

Clang's StaticAnalyzer seems to (correctly) complain about code like:

    T *p = calloc(sizeof(U), N);

...Where T and U are different types.

This patch removes some instances of this pattern from compiler-rt.

Patch by Apelete Seketeli.
Differential Revision: http://reviews.llvm.org/D19085

llvm-svn: 266388