First take at trying to enable precompiled headers.
Ignore cotire's files.
Remove some hardcoded paths.
Remove the hardcoded path to the architecture-specific libc directory.
Remove compile warnings when compiling with PCH on.
Merge branch 'master' into lowjoel-pch
More include paths which need disabling.
Fix path detection of LibC architecture-specific paths on Ubuntu 12.04.
libxml does not need an exclusion.
Merge remote-tracking branch 'upstream/master' into lowjoel-pch
Declare the paths for Cotire to ignore only after we have detected all their paths.

jemalloc was not detected in the directory above.
Merge remote-tracking branch 'upstream/master' into lowjoel-pch
Revert "Remove compile warnings when compiling with PCH on."

This reverts commit e36d8bcefca47d071f4bdeb3b8b76e9911caee8e.
Remove compile warnings when compiling with PCH on.
Fix another macro redefinition warning.
Merge branch 'lowjoel-pch' into lowjoel-drupal7
Merge branch 'lowjoel-fix-1932-warnings' into lowjoel-drupal7
Have a separate warning level for predefined classes' instance methods when verifying argument count.

Fixes #1952. Zend does not warn when this happens. Hence, the warning is now emitted only when using HipHop Syntax.