Clean up Verilator sections in core files

- The "PINCONNECTEMPTY" waiver is part of our normal waiver file, no need
  to add it to the tool invocation.
- Recent versions of Verilator choose good defaults for MAKE_OPTS,
  passing it explicitly overrides the settings.
- All Verilator code is now lint clean, we can remove `-Wno-fatal`.
- FST traces are not much slower then VCD traces any more in recent
  Verilator versions, remove the respective comment.
- Align comment about the compile/sim time for tracing with other files
  and OpenTitan.

dv/cs_registers/tb_cs_registers.core

@@ -118,19 +118,9 @@ targets:
           # huge influence on runtime performance.
           - '--trace'
           - '--trace-fst' # this requires -DVM_TRACE_FMT_FST in CFLAGS below!
-          # Remove FST options for VCD trace (~100 x faster but larger files)
           - '--trace-structs'
           - '--trace-params'
           - '--trace-max-array 1024'
           - '-CFLAGS "-std=c++14 -Wall -DTOPLEVEL_NAME=tb_cs_registers -DVM_TRACE_FMT_FST -g"'
           - '-LDFLAGS "-pthread -lutil -lelf"'
           - "-Wall"
-          - "-Wno-PINCONNECTEMPTY"
-          # XXX: Cleanup all warnings and remove this option
-          # (or make it more fine-grained at least)
-          - "-Wno-fatal"
-        make_options:
-          # Optimization levels have a large impact on the runtime performance
-          # of the simulation model. -O2 and -O3 are pretty similar, -Os is
-          # slower than -O2/-O3
-          - OPT_FAST="-O2"

dv/riscv_compliance/ibex_riscv_compliance.core

@@ -103,19 +103,9 @@ targets:
           # huge influence on runtime performance.
           - '--trace'
           - '--trace-fst' # this requires -DVM_TRACE_FMT_FST in CFLAGS below!
-          # Remove FST options for VCD trace (~100 x faster but larger files)
           - '--trace-structs'
           - '--trace-params'
           - '--trace-max-array 1024'
           - '-CFLAGS "-std=c++11 -Wall -DVM_TRACE_FMT_FST -DTOPLEVEL_NAME=ibex_riscv_compliance -g"'
           - '-LDFLAGS "-pthread -lutil -lelf"'
           - "-Wall"
-          - "-Wno-PINCONNECTEMPTY"
-          # XXX: Cleanup all warnings and remove this option
-          # (or make it more fine-grained at least)
-          - "-Wno-fatal"
-        make_options:
-          # Optimization levels have a large impact on the runtime performance
-          # of the simulation model. -O2 and -O3 are pretty similar, -Os is
-          # slower than -O2/-O3
-          - OPT_FAST="-O2"

examples/simple_system/ibex_simple_system.core

@@ -123,25 +123,16 @@ targets:
       verilator:
         mode: cc
         verilator_options:
-# Disabling tracing reduces compile times by multiple times, but doesn't have a
-# huge influence on runtime performance. (Based on early observations.)
+          # Disabling tracing reduces compile times but doesn't have a
+          # huge influence on runtime performance.
           - '--trace'
           - '--trace-fst' # this requires -DVM_TRACE_FMT_FST in CFLAGS below!
           - '--trace-structs'
           - '--trace-params'
           - '--trace-max-array 1024'
-# compiler flags
-#
-# -O
-#   Optimization levels have a large impact on the runtime performance of the
-#   simulation model. -O2 and -O3 are pretty similar, -Os is slower than -O2/-O3
-          - '-CFLAGS "-std=c++11 -Wall -DVM_TRACE_FMT_FST -DTOPLEVEL_NAME=ibex_simple_system -g -O0"'
+          - '-CFLAGS "-std=c++11 -Wall -DVM_TRACE_FMT_FST -DTOPLEVEL_NAME=ibex_simple_system -g"'
           - '-LDFLAGS "-pthread -lutil -lelf"'
           - "-Wall"
-          - "-Wno-PINCONNECTEMPTY"
-          # XXX: Cleanup all warnings and remove this option
-          # (or make it more fine-grained at least)
-          - "-Wno-fatal"
           # RAM primitives wider than 64bit (required for ECC) fail to build in
           # Verilator without increasing the unroll count (see Verilator#1266)
           - "--unroll-count 72"