Print concise summaries instead of full commands for some of the most verbose
commands.  For example, print
```
OCAMLC lambda/switch.cmo
```
instead of
```
./boot/ocamlrun ./boot/ocamlc -nostdlib -I ./boot -use-prims runtime/primitives -g -strict-sequence -principal -absname -w +a-4-9-40-41-42-44-45-48 -warn-error +a -bin-annot -strict-formats -I lambda -I utils -I parsing -I typing -I bytecomp -I file_formats -I lambda -I middle_end -I middle_end/closure -I middle_end/flambda -I middle_end/flambda/base_types -I asmcomp -I driver -I toplevel -I tools -c lambda/switch.ml
```
and
```
CC runtime/addrmap.b.o
```
instead of
```
gcc -c -O2 -fno-strict-aliasing -fwrapv -pthread -g -Wall -Werror -fno-common -fexcess-precision=standard -fno-tree-vrp -ffunction-sections  -I./runtime  -D_FILE_OFFSET_BITS=64  -DCAMLDLLIMPORT= -DIN_CAML_RUNTIME  -o runtime/addrmap.b.o runtime/addrmap.c
```

The output is generated with the Make function `$(info ...)` to avoid shelling
out to `echo` each time, which can be expensive under Cygwin.

A variable `V` controls whether to use the new style. When `V=0` (the default),
it is used. If `V=1`, then the usual full output is used instead.

Co-authored-by: Nicolás Ojeda Bär <n.oje.bar@gmail.com>

Sort the index of modules in the API documentation in the following
order
- text documentation
- non-internal modules
- internal modules
In each subcategory, the modules are sorted in alphabetical order

The configure script sets this variable to "true" if the runtime_events
library has to be built. At the moment it is always built but this may
change.