Nim toolchain improvements

- Fix fatal exception handling so that stack traces are dumped
- Add 'include/nim' directories to Nim module search path
- Enable release optimizations for release builds

Fix #2493

repos/base/mk/generic.mk

@@ -97,6 +97,8 @@ else
 NIM_MAKEFILES := $(foreach X,$(SRC_NIM),$(X).mk)
 NIM_ARGS  = --compileOnly --os:genode --cpu:$(NIM_CPU)
 NIM_ARGS += --verbosity:0 --hint[Processing]:off --nimcache:.
+NIM_ARGS += --noCppExceptions
+NIM_ARGS += $(foreach X,$(call select_from_repositories,include/nim),--path:$(X))
 NIM_ARGS += $(NIM_OPT)
 
 # Generate the C++ sources and compilation info

repos/base/mk/spec/release.mk

@@ -1 +1,2 @@
 CC_OPT += -DGENODE_RELEASE
+NIM_ARGS += -d:release