Upgrading autoconf
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If you are in the mood to upgrade autoconf, you should:
1. Consider not upgrading.
2. No really, this is a hassle, you don't want to do it.
3. Get the new version of autoconf and put it in <SRC>
4. configure/build/install autoconf with --prefix=<PFX>
5. Run autoupdate on all the m4 macros in llvm/autoconf/m4
6. Run autoupdate on llvm/autoconf/configure.ac
7. Regenerate configure script with AutoRegen.sh
8. If there are any warnings from AutoRegen.sh, fix them and go to step 7.
9. Test, test, test.
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