OS X

After upgrading OS X from 10.7 to 10.8 or 10.8 to 10.9, it seems necessary to reinstall the Apple Developer Tools "Command Line Tools". Something like this will happen:

$ ./configure --prefix=$HOME/src LDFLAGS=-L$HOME/src/lib CFLAGS=$HOME/src/include
checking build system type... i386-apple-darwin13.0.0
checking host system type... i386-apple-darwin13.0.0
checking target system type... i386-apple-darwin13.0.0
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... ./install-sh -c -d
checking for gawk... no
checking for mawk... no
checking for nawk... no
checking for awk... awk
checking whether make sets $(MAKE)... yes
checking for gcc... gcc
checking for C compiler default output file name... 
configure: error: in `/Users/andy/src/bwtool':
configure: error: C compiler cannot create executables
See `config.log' for more details.

There's a quick way to find the right download. Open XCode and go to "More Developer Tools":

Then you'll see it:

Install whichever Command-line Tools fits your setup and hopefully things will be working again.