Review multilibs being used for gcc

Right now we are building the following multilibs for gcc:

• rv32e-ilp32e
• rv32i-ilp32
• rv32im-ilp32
• rv32iac-ilp32
• rv32imac-ilp32
• rv32imafc-ilp32f
• rv32imafdc-ilp32d
• rv64i-lp64
• rv64ic-lp64
• rv64iac-lp64
• rv64imac-lp64
• rv64imafdc-lp64d
• rv64im-lp64

Notably absent is anything related to bit manipulation, crypto, zifencei, and zfh, but many other extensions that we use are also missing. It is probably worth reviewing these and at least adding multilib configurations that match each of the main CVW configs.