v1.6.1: Faster routing, fixed yosys-abc9

This release updates all of the included tools:

• nextpnr-ecp5 now performs routing faster when the dsp is in use.
• The -abc9 parameter in yosys no longer crashes on Windows.
• wishbone-tool has been updated, fixing some bugs in the riscv debugger and making it more reliable.
• Gcc and the Risc-V toolchain are updated to their 2019.08-8.3.0 releases.
• Regenerate bba files on Windows (fixes toolchain release v1.6)