Disable the strict-aliasing warnings produced by gcc

GCC produce a lot of strict-aliasing warning for the LLDB codebase
what makes reading the compile output very difficult. This change
disable these warnings to reduce the noise as we already ignore them.

We should consider re-enabling the warning if we fix all (or most)
strict-aliasing violation first.

Differential revision: http://reviews.llvm.org/D13981

llvm-svn: 251107