Add support for Link Time Optimization (LTO) on gcc and Clang.
Link libssp only when it is on the system, some toolchains like Ubuntu's
do not require explicitly linking to libssp. On Win32 try to link it
statically.
In debug builds with GCC, use -ggdb3 -Og, otherwise use -g .
Two new cmake modules were written for this:
* FindSSP.cmake -- this is for finding libssp on the system.
* UseGCCBinUtilsWrappers.cmake -- this is for using gcc binutils
wrappers such as gcc-ar, which is required for gcc LTO to work.
These will be distributed separately as well.
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