On my Windows 8 system: 16/10/2012 07:45 119,296 libgcc_s_dw2-1.dll
The dll does not contain any version information, but gcc --version prints 4.7.2.
On my Windows XP system where it works: 05/10/2013 12:17 PM 112,142 libgcc_s_dw2-1.dll
gcc 4.8.1 is installed.
On my Windows 8 system, I renamed the DLL. Unexpectedly emacs launched, and it exited normally. According to Process Monitor, emacs failed to find this DLL anywhere else. I doubt that I have another copy but I am searching the C: drive now.