what is difference between gcc version and Xcode gcc version?

This maybe a little silly question but I am very confused

executing pkgutil in shell I get

$ pkgutil --pkg-info=com.apple.pkg.CLTools_Executables
package-id: com.apple.pkg.CLTools_Executables
version: 6.1.1.0.1.1416017670

the above tells me version 6.1

and gcc version in shell tells

$ gcc --version
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin13.1.0
Thread model: posix

This says LLVM version 6.0 , Can anyone explains what the above versions are telling are which version of what !!