Add SONAME for libc.so

Usually it is possible to refer to library either by the file name or by
elf "soname" soname is very similar for specifying something like
(LIB/API version) combination so if for example you have ./prog that
loads libx.so which is version 5.1.1 and there is ./plugin.so that ./prog
would load that requires libx.so version 5.1.2 both libx.so should have
the same soname to hint that they offer the exact same functionality.
And this patch specifies the soname for relibc libc.so.

Makefile

@@ -110,7 +110,7 @@ $(BUILD)/debug/libc.a: $(BUILD)/debug/librelibc.a $(BUILD)/pthreads-emb/libpthre
 	$(AR) -M < "$@.mri"
 
 $(BUILD)/debug/libc.so: $(BUILD)/debug/librelibc.a $(BUILD)/pthreads-emb/libpthread.a $(BUILD)/openlibm/libopenlibm.a
-	$(CC) -nostdlib -shared -Wl,--allow-multiple-definition -Wl,--whole-archive $^ -Wl,--no-whole-archive -o $@
+	$(CC) -nostdlib -shared -Wl,--allow-multiple-definition -Wl,--whole-archive $^ -Wl,--no-whole-archive -Wl,-soname,libc.so.6 -o $@
 
 $(BUILD)/debug/librelibc.a: $(SRC)
 	CARGO_INCREMENTAL=0 $(CARGO) rustc $(CARGOFLAGS) -- --emit link=$@ $(RUSTCFLAGS)
@@ -149,7 +149,7 @@ $(BUILD)/release/libc.a: $(BUILD)/release/librelibc.a $(BUILD)/pthreads-emb/libp
 	$(AR) -M < "$@.mri"
 
 $(BUILD)/release/libc.so: $(BUILD)/release/librelibc.a $(BUILD)/pthreads-emb/libpthread.a $(BUILD)/openlibm/libopenlibm.a
-	$(CC) -nostdlib -shared -Wl,--allow-multiple-definition -Wl,--whole-archive $^ -Wl,--no-whole-archive -o $@
+	$(CC) -nostdlib -shared -Wl,--allow-multiple-definition -Wl,--whole-archive $^ -Wl,--no-whole-archive -Wl,-soname,libc.so.6 -o $@
 
 $(BUILD)/release/librelibc.a: $(SRC)
 	CARGO_INCREMENTAL=0 $(CARGO) rustc --release $(CARGOFLAGS) -- --emit link=$@ $(RUSTCFLAGS)