RVCT (ARM Real View Compilation Tools) is the compiler tools provided by ARM corporation. It can generate ABI (Application Binary Interface) V1 and V2 target versions.
GCCE (GNU C Compiler Embedded) is a CSL ARM ToolChain included in UIQ SDK, which only supports ABI V2.
RVCT has better performance than GCCE since it's optimized by ARM Corp. GCCE then is more strict on codes, e.g. more careful checks on grammar. Binary generated by RVCT is normally smaller than GCCE.
Code built with GCCE can inter-operate with code built by other compilers to ABIv2; in particular, with code built using ARM RVCT 2.2 using the ABIv2 version of the ARMV5 target. GCCE built code is not compatible with code built to ABIv1 using ARM RVCT 2.1.
For more detail explanations on GCCE, refer to Symbian technical article http://developer.uiq.com/devlib/uiq_30/SDKDocumentation/sdl/N1035A/BuildTools/native/gcce.html