I noticed after upgrading to Yosemite that none of my upgrades in homebrew would work anymore.
I noticed that it was a problem in general with compiling any kind of C code.
The error I get is:
In file included from /usr/include/stdio.h:75: /usr/include/sys/stdio.h:39:52: error: expected function body after function declarator int renameat(int, const char *, int, const char *) __OSX_AVAILABLE_STARTING(__MAC_10_10, __IPHONE_8_0); ^ /usr/local/include/Availability.h:159:50: note: expanded from macro '__OSX_AVAILABLE_STARTING' #define __OSX_AVAILABLE_STARTING(_osx, _ios) __AVAILABILITY_INTERNAL##_osx ^ <scratch space>:61:1: note: expanded from here __AVAILABILITY_INTERNAL__MAC_10_10
I get this with every C code I try.
I updated XCode to 6.2, and the command line tools as well.
The strange thing is, this is on my mac mini, but my MacBook Pro does not have this issue at all.