From Forum Nokia Wiki

The ARMV5 build target, supported for EKA2-based releases of the OS from 8.1b, builds to the ARMv5 architecture. It is not built using the GNU GCC compiler supplied on Symbian OS kits. Instead, the intention is that code is built to conform to a binary standard developed by ARM (the ABI for the ARM architecture).

• Reference Link: ARMV5 build target