catch-up after a two years hiatus

- drop Travis support (now defunct)
- generic_cpp.mk: use -std=c++17 (requires gcc 7.3 or later)
- RlinkPortCuff : drop libusb_set_debug (now deprecated)
- viv_tools_config.tcl: use open_hw_manager
- vbomconv: ghdl_m: use -Wl,--no-pie (for UB 18.04 gcc)
- simlib.vhd: write{oct,hex}: fix for ghdl V0.36 -Whide warnings

rtl/.gitignore

@@ -53,3 +53,6 @@ tmu_ofile
 *.tap
 *.lst
 *.cof
+
+# saved synthesis
+viv_20??.*