RMagick installs using devkits msys.bat but not using gitbash

(I am using Windows 8)

I finally got the rmagick gem to install by opening the msys.bat file in my Devkit folder using this command

gem install rmagick --platform=ruby -- --with-opt-lib=c:/imagemagick/lib --with-opt-include=c:/imagemagick/include

This is the output

Building native extensions with: '--with-opt-lib=c:/imagemagick/lib --with-opt-i
nclude=c:/imagemagick/include'
This could take a while...
Successfully installed rmagick-2.15.0
Parsing documentation for rmagick-2.15.0
Done installing documentation for rmagick after 6 seconds
1 gem installed

But when I run the same exact command using gitbash I get this error:

Temporarily enhancing PATH to include DevKit...
Building native extensions with: '--with-opt-lib=c:/imagemagick/lib --with-opt-include=c:/imagemagick/include'
This could take a while...
ERROR:  Error installing rmagick:
        ERROR: Failed to build gem native extension.

    c:/RailsInstaller/Ruby2.1.0/bin/ruby.exe extconf.rb --with-opt-lib=c:/imagemagick/lib --with-opt-include=c:/imagemagick/include
Invalid drive specification.
Unable to get ImageMagick version
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include=${opt-dir}/include
        --with-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=c:/RailsInstaller/Ruby2.1.0/bin/ruby

extconf failed, exit code 1

Gem files will remain installed in c:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/rmagick-2.15.0 for inspection.
Results logged to c:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/extensions/x86-mingw32/2.1.0/rmagick-2.15.0/gem_make.out

I get this same exact error when running bundle install using gitbash and when I try to run bundle install using msys.bat I get the same error but its a bit longer and complains about development tools.

If it works using msys.bat, what do I need to change to get it to work with gitbash and with bundle installs?