I found that other people too have had trouble in installing Meld to Mac by MacPorts.
I run
sudo port install meld
I get
sudo port install meld
---> Activating shared-mime-info @0.60_0
Error: Target org.macports.activate returned: Image error: /opt/local/bin/update-mime-database already exists and does not belong to a registered port. Unable to activate port shared-mime-info.
Error: The following dependencies failed to build: py25-gnome gconf gtk2 shared-mime-info orbit2 libidl gnome-vfs desktop-file-utils gnome-mime-data libbonobo libbonoboui libglade2 libgnome esound audiofile libgnomecanvas libart_lgpl libgnomeui gnome-icon-theme hicolor-icon-theme icon-naming-utils p5-xml-simple p5-xml-namespacesupport p5-xml-sax gnome-keyring libtasn1 py25-gtk py25-cairo py25-numpy py25-nose py25-gobject py25-orbit
Error: Status 1 encountered during processing.
How can you install Meld to Mac?
I found that MacPorts worked to install meld, but it didn't work straight away as advertised.
After running and installing all the dependencies, it failed, and gave a cryptic log message similar to the one in this question (but not identical).
After a bit of digging around I found I had to do the following:
Make sure I had properly agreed to the license for XCode
xcodebuild -license
Install the Xcode command line tools
xcode-select --install
Install rarian (it seems to be a dependency that MacPorts failed to recognize)
sudo port install rarian
The latter instructions come from here: http://www.codez.co.uk/2014/02/meld-on-mac-osx-mavericks-10-9/ and this was the last step before I was able to get it working.