After upgrading to Xcode7 and Command Line Tools 10.10, I can't compile standard programs anymore. The error is (from the cputhrottle package):
/tmp/cputhrottle% make /usr/bin/g++ -c -g -Wall -I..///boost_1_43_0 cputhrottle.cc In file included from cputhrottle.cc:5: In file included from ./manip.h:4: In file included from /usr/local/include/boost/shared_ptr.hpp:17: In file included from /usr/local/include/boost/smart_ptr/shared_ptr.hpp:17: In file included from /usr/local/include/boost/config.hpp:44: In file included from /usr/local/include/boost/config/select_stdlib_config.hpp:18: In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cstddef:36: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__config:23:10: fatal error: 'unistd.h' file not found #include <unistd.h> ^ 1 error generated. make: *** [cputhrottle.o] Error 1
Downloading and installed the Command Line Tools 10.10 for Xcode 6.4 fixed it, though.