Using uname fails e.g. on a 64-bit machine with a 32-bit toolchain.
The following gcc -dumpmachine strings have been verified:
* 32-bit Linux gives i486-linux-gnu
* 64-bit Linux gives x86_64-linux-gnu
* Mac OS X 10.5 gives i686-apple-darwin9
* MinGW gives mingw32
*darwin8* and *bsd* can safely be assumed to be correct, but *cygwin*
is a guess.
Change-Id: I6bef2ab5e97cbd3410aa66b0c4f84d2231884b05
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