Add support for LTO and Gold linker (#1812)

This commit add (optional) support for Link-Time-Optimization and Gold
linker.
This is the first, mandatory step needed to make nDPI compliant with
"introspector" sanitizer requirements in OSS-Fuzz: see
https://github.com/google/oss-fuzz/issues/8939

Gold linker is not supported by Windows and by macOS, so this feature is
disabled by default. It has been enable in CI in two linux targets
("latest" gcc and clang).

Fix some warnings triggered by LTO.

The changes in `src/lib/ndpi_serializer.c` seams reasonable.
However, the change in `tests/unit/unit.c` is due to the following
warning, which seems to be a false positive.

```
unit.c: In function ‘serializerUnitTest’:
ndpi_serializer.c:2258:13: error: ‘MEM[(struct ndpi_private_serializer *)&deserializer].buffer.size’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
unit.c:67:31: note: ‘MEM[(struct ndpi_private_serializer *)&deserializer].buffer.size’ was declared here
   67 |   ndpi_serializer serializer, deserializer;
      |                               ^
ndpi_serializer.c:2605:10: error: ‘MEM[(struct ndpi_private_serializer *)&deserializer].status.buffer.size_used’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
unit.c:67:31: note: ‘MEM[(struct ndpi_private_serializer *)&deserializer].status.buffer.size_used’ was declared here
   67 |   ndpi_serializer serializer, deserializer;
```
Since this warning is triggered only with an old version of gcc and
`tests/unit/unit.c` is used only during the tests, the easiest fix has
been applied.

Some (unknown to me) combinations of OS and compiler trigger the
following warnings at linker time (with sanitizer and gold linker)
```
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_load1_asm'
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_load2_asm'
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_load4_asm'
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_load8_asm'
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_load16_asm'
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_store1_asm'
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_store2_asm'
/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_report_store4_asm'
[..]
```
I have not found any references to this kind of message, with the only
exception of https://sourceware.org/bugzilla/show_bug.cgi?id=25975
which seems to suggest that these messages can be safely ignored.
In any case, the compilation results are sound.

Fix `clean` target in the Makefile in the `example` directory.

In OSS-Fuzz enviroments, `fuzz_ndpi_reader` reports a strange link error
(as always, when the gold linker is involved...).
It's come out that the culprit was the `tempnam` function: the code has
been changed to use `tmpfile` instead. No sure why... :(

Fuzzing target `fuzz_ndpi_reader.c` doesn't use `libndpiReader.a`
anymore: this way we can use `--with-only-libndpi` flag on Oss-Fuzz builds
as workaround for the "missing dependencies errors" described in
https://github.com/google/oss-fuzz/issues/8939

1 files changed, 1 insertions, 1 deletions

diff --git a/example/Makefile.in b/example/Makefile.in
index 73bc51986..d6dbaa21a 100644
--- a/example/Makefile.in
+++ b/example/Makefile.in
@@ -79,7 +79,7 @@ cppcheck:
 	 cppcheck --template='{file}:{line}:{severity}:{message}' --quiet --enable=all --force -I$(SRCHOME)/include *.c
 
 clean:
-	/bin/rm -f *.o ndpiReader ndpiSimpleIntegration ndpiReader$(EXE_SUFFIX) ndpiSimpleIntegration$(EXE_SUFFIX) ndpiReader.dpdk
+	/bin/rm -f *.o ndpiReader ndpiSimpleIntegration ndpiReader$(EXE_SUFFIX) ndpiSimpleIntegration$(EXE_SUFFIX) ndpiReader.dpdk libndpiReader.a
 	/bin/rm -f .*.dpdk.cmd .*.o.cmd *.dpdk.map .*.o.d
 	/bin/rm -f _install _postbuild _postinstall _preinstall
 	/bin/rm -rf build