golang revel app failing to compile after upgrading OSX command line tools - macos

Question

i was playing around with the revel sample bookings app (http://robfig.github.io/revel/samples/booking.html) and everything was working fine.
after upgrading my OSX command line tools from the apple developer site, the app refuses to start:
INFO 2014/03/10 23:33:46 harness.go:165: Listening on :9000
TRACE 2014/03/10 23:34:00 harness.go:126: Rebuild
TRACE 2014/03/10 23:34:00 build.go:127: Exec: [/usr/local/bin/git describe --always --dirty]
TRACE 2014/03/10 23:34:00 build.go:77: Exec: [/usr/local/bin/go build -ldflags -X github.com/robfig/revel/samples/booking/app.APP_VERSION "git-930a54f" -tags gorp -o /Users/nrser/dev/gopath/bin/booking github.com/robfig/revel/samples/booking/app/tmp]
ERROR 2014/03/10 23:34:02 build.go:84: # github.com/robfig/revel/samples/booking/app/tmp
xcrun: Error: failed to exec real xcrun. (No such file or directory)
go install github.com/robfig/revel/samples/booking/app/tmp: build output "/Users/nrser/dev/gopath/bin/booking" already exists and is not an object file
ERROR 2014/03/10 23:34:02 build.go:247: Failed to parse build errors:
# github.com/robfig/revel/samples/booking/app/tmp
xcrun: Error: failed to exec real xcrun. (No such file or directory)
go install github.com/robfig/revel/samples/booking/app/tmp: build output "/Users/nrser/dev/gopath/bin/booking" already exists and is not an object file
i tried rm /Users/nrser/dev/gopath/bin/booking, but then get this when attempting revel run github.com/robfig/revel/samples/booking:
INFO 2014/03/10 23:38:13 harness.go:165: Listening on :9000
TRACE 2014/03/10 23:38:16 harness.go:126: Rebuild
TRACE 2014/03/10 23:38:16 build.go:127: Exec: [/usr/local/bin/git describe --always --dirty]
TRACE 2014/03/10 23:38:16 build.go:77: Exec: [/usr/local/bin/go build -ldflags -X github.com/robfig/revel/samples/booking/app.APP_VERSION "git-930a54f" -tags gorp -o /Users/nrser/dev/gopath/bin/booking github.com/robfig/revel/samples/booking/app/tmp]
TRACE 2014/03/10 23:38:18 app.go:56: Exec app: /Users/nrser/dev/gopath/bin/booking [/Users/nrser/dev/gopath/bin/booking -port=56507 -importPath=github.com/robfig/revel/samples/booking -runMode=dev]
ERROR 2014/03/10 23:38:18 app.go:58: Error running: fork/exec /Users/nrser/dev/gopath/bin/booking: exec format error
i'm assuming this has something to do with some stuff being built using the old command line tools and some stuff with the new version, but i don't know how to clean the binaries out or force a rebuild of all the packages or whatever would be required. any help much appreciated.
some possibly relevant dumps:
uname -a
Darwin mba2 12.5.0 Darwin Kernel Version 12.5.0: Sun Sep 29 13:33:47 PDT 2013; root:xnu-2050.48.12~1/RELEASE_X86_64 x86_64
go env
GOARCH="amd64"
GOBIN=""
GOCHAR="6"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/nrser/dev/gopath"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.2/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.2/libexec/pkg/tool/darwin_amd64"
TERM="dumb"
CC="/usr/local/bin/gcc-4.2"
GOGCCFLAGS="-g -O2 -fPIC -m64 -pthread -fno-common"
CXX="clang++"
CGO_ENABLED="1"
go was just installed via homebrew,
go version
go version go1.2 darwin/amd64