Prior to 4.6.0, -Wshadow would cause GCC to warn when variables shadowed
global functions. Since libc defines a number of functions with common
names, this is a problem. Also, without this change, we'll keep breaking
on older versions of GCC because we won't be testing with them.
OpenBSD, specifically is reported to have a problem:
https://boringssl-review.googlesource.com/#/c/2900/
(Note the test should really be >= 4.6.0, but CMake doesn't have a
VERSION_GREATEROREQUAL.)
Change-Id: I1aedda01ab629e138c8781e4319bfaaed0b236b0
Reviewed-on: https://boringssl-review.googlesource.com/2952
Reviewed-by: Adam Langley <agl@google.com>
07100c6e69