UPDATE October 23 2013 As commenters point out below, simply installing Xcode 5.0.1 and its Command Line Tools is enough. I’ve finally got around to testing out the suggestion provided to me almost two weeks ago, and it worked.
The content below is preserved for posterity. Please just install Command Line Tools and see if that helps.
Is perhaps brew install serf or brew install subversion broken for you on Mavericks? Or generally apr-1-config seems to return spurious results referring to nonexistent locations in /usr/include or to OSX10.9.xctoolchain?
While Apple does not recommend touching any system file or folder as they may and will be overwritten during OS upgrade, consider editing the following lines:
-prefix="/usr" +prefix="/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr" -CC="/Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.9.xctoolchain/usr/bin/cc" -CPP="/Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.9.xctoolchain/usr/bin/cc -E" +CC="/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc" +CPP="/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc -E"
Now that I have serf package installed, all I have left to figure out (or get someone else to figure out!) is subversion. Only then I might have some hope of getting hgsubversion to work again and getting some work done without resorting to Subversion directly.
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via blog.vucica.net
The breakage is because Xcode's command line tools weren't installed, or at least weren't upgraded with an upgrade to Mavericks.
Command line tools can be installed via dpkg or via
xcode-select --install.I was able to install serf without doing this by installing the Mavericks Command-line Tools (no longer installable from inside XCode, apparently). See the end of this homebrew ticket.