ld: can't write output file: pstree for architecture x86_64

[macports@…]

# port install pstree
--->  Fetching archive for pstree
--->  Attempting to fetch pstree-2.33_1.darwin_11.x86_64.tbz2 from http://packages.macports.org/pstree
--->  Fetching pstree
--->  Verifying checksum(s) for pstree
--->  Extracting pstree
--->  Configuring pstree
--->  Building pstree
--->  Staging pstree into destroot
unable to read unknown load command 0x24
unable to read unknown load command 0x26
--->  Installing pstree @2.33_1
--->  Activating pstree @2.33_1
--->  Cleaning pstree

# pstree 
-sh: /opt/local/bin/pstree: Malformed Mach-o file

# file /opt/local/bin/pstree
/opt/local/bin/pstree: Mach-O executable x86_64

In main.log we have:

:debug:build Executing org.macports.build (pstree)
:debug:build Environment: CPATH='/opt/local/include' CC_PRINT_OPTIONS_FILE='/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/work/.CC_PRINT_OPTIONS' LIBRARY_PATH='/opt/local/lib' CC_PRINT_OPTIONS='YES' MACOSX_DEPLOYMENT_TARGET='10.7' GI_SCANNER_DISABLE_CACHE='1'
:debug:build Assembled command: 'cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/work/pstree-2.33" && /usr/bin/make -j2 -w all'
:debug:build Executing command line:  cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/work/pstree-2.33" && /usr/bin/make -j2 -w all 
:info:build make: Entering directory `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/work/pstree-2.33'
:info:build /usr/bin/clang -pipe -O1 -arch x86_64 -I/opt/local/include -L/opt/local/lib -arch x86_64 pstree.c -o pstree
:info:build ld: can't write output file: pstree for architecture x86_64
:info:build clang: error: linker command failed with exit code 1 (use -v to see invocation)
:info:build make: *** [all] Error 1
:info:build make: Leaving directory `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/work/pstree-2.33'
:info:build shell command " cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/work/pstree-2.33" && /usr/bin/make -j2 -w all " returned error 2
:error:build Target org.macports.build returned: shell command failed (see log for details)
:debug:build Backtrace: shell command failed (see log for details)
    while executing
"command_exec build"
    (procedure "portbuild::build_main" line 8)
    invoked from within
"$procedure $targetname"
:info:build Warning: the following items did not execute (for pstree): org.macports.activate org.macports.build org.macports.destroot org.macports.install
:notice:build Log for pstree is at: /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/main.log

When omitting the "install" part, things seem to work:

# port build pstree
--->  Fetching pstree
--->  Verifying checksum(s) for pstree
--->  Extracting pstree
--->  Configuring pstree
--->  Building pstree

#  /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_sysutils_pstree/pstree/work/pstree-2.33/pstree | head -2
-+= 00001 root /sbin/launchd
 |--= 00010 root /usr/libexec/kextd

[macports@…]

port install pstree

[ryandesign (Ryan Carsten Schmidt)]

It sounds like Xcode may not be installed properly. Could you uninstall and reinstall Xcode?