How to use scandeps_server to auto-get the c/c++ includes

Hello everyone! I want to use reclient as an client and connect to buildfarm for remote execution.

- Start the reproxy:

```
./bootstrap -cfg=/path/to/reproxy.cfg
```
The reproxy.cfg is:
```
service=xx.xxx.xxx.xxx:xxx
server_address=unix:///tmp/reproxy.sock
instance=main
fail_early_min_action_count=4000
fail_early_min_fallback_ratio=0.5
service_no_security=true
service_no_auth=true
use_rpc_credentials=false
use_gce_credentials=false
use_application_default_credentials=false
output_dir=/path/to/out
proxy_log_dir=/path/to/out
```
- Wrap the gcc:

```makefile
CC=$(rewrapper_path) -cfg=$(rewrapper_cfg_path) gcc

CFLAGS=-I. -I/usr/lib/gcc/x86_64-linux-gnu/11/include
OBJ = hellomake.o hellofunc.o

%.o:%.c
$(CC) -c $(CFLAGS) -o $@ $<
hellomake: $(OBJ)
$(CC) -o $@ $^
```
The rewrapper.cfg is:
```
exec_strategy=remote
server_address=unix:///tmp/reproxy.sock
exec_root=/path/to/reclient_test
inputs=hellofunc.c,hellomake.c
output_files=hellofunc.o,hellomake.o
download_outputs=true
```
I hope that the scandeps_server in the same directory as reproxy can search and upload the includes of `.c` files to buildfarm. However, the remote execution returns error as:
```
hellomake.c:1:9: fatal error: hellomake.h: No such file or directory
1 | #include
| ^~~~~~~~~~~~~
compilation terminated.
make: *** [makefile:11: hellomake.o] Error 1
```
where, hellomake.h is in the exec_root. If I want to successfully implement a remote build, I have to add all needed srcs and headers to the `-inputs`, but the included headers are often difficult to obtain in advance. The directory structure of the demo is as follows:
```
|-- hellofunc.c
|-- hellomake.c
|-- hellomake.h
|-- makefile
|-- out
`-- rbe
|-- bin
| |-- bigquery
| |-- bootstrap
| |-- downloadmismatch
| |-- dumpstats
| |-- logdump
| |-- metricsuploader
| |-- reclientreport
| |-- reproxy
| |-- reproxystatus
| |-- reproxytool
| |-- rewrapper
| |-- rpl2cloudtrace
| |-- rpl2trace
| `-- scandeps_server
`-- configs
|-- reproxy.cfg
`-- rewrapper.cfg
```

How to use reclient without setting rewrapper's `-inputs` and `-output_files` parameters?

Reproduce the remote build described by the Makefile and the reproxy.cfg and rewrapper.cfg files, starting with the scandeps_server entry point and the rewrapper inputs and output_files settings. Done should establish whether included headers can be discovered and uploaded automatically without manually listing those parameters.

Written by the indexing model from the issue text.