Cygwin g++ --unresolved-symbols=ignore-all - c++

Question

I have a simple proof case file, which is called main.c
void bar(void);
void foo(void)
{
bar();
}
int main(void)
{
return 0;
}
As you can see there is no definition for bar()
My goal is to compile this on windows using cygwin's gcc.
I have figured out that I could use the following linker option:
--unresolved-symbols=ignore-all
This should tell the linker not to care about missing symbols. In the main.c example the missing symbol would not even be an issue, as foo is never called, therefore there should not be an undefined behavior when the program is executed.
I have 2 flavors of gcc, one for embedded ARM targets, and one from cygwin 64bit for windows.
The embedded ARM gcc is from here: https://developer.arm.com/open-source/gnu-toolchain/gnu-rm , version 4_9-2015q3.
The Cygwin gcc is taken from https://cygwin.com 's 64bit installer, version 7.3.0-1
I use these compile options with the compilers:
arm-none-eabi-g++.exe -Wl,--unresolved-symbols=ignore-all main.c
g++.exe -Wl,--unresolved-symbols=ignore-all main.c
The first compiles and links without errors, as for the second I get this error message:
/cygdrive/c/Users/user/AppData/Local/Temp/ccRF8tf5.o:main.c:(.text+0x9): undefined reference to `bar()'
/cygdrive/c/Users/user/AppData/Local/Temp/ccRF8tf5.o:main.c:(.text+0x9): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `bar()'
collect2: error: ld returned 1 exit status
Where clearly the undefined reference to `bar()' message should have been suppressed by the option -Wl,--unresolved-symbols=ignore-all
(The second error message does not appear, if I use gcc from the 32 bit cygwin installer.)
The --help command for the cygwin ld shows the --unresolved-symbols=ignore-all as a valid option.
I suppose the cygwin gcc has been compiled in a way, that this option does not work, even though it is not complaining that it can not validate this option.
If for example I use this command:
g++.exe -Wl,--unresolved-symbols=dummy main.c
I get this error message:
/usr/lib/gcc/x86_64-pc-cygwin/7.3.0/../../../../x86_64-pc-cygwin/bin/ld: bad --unresolved-symbols option: dummy
Which for me tells, that --unresolved-symbols is in fact is an accepted command.
My questions would be:
Is there a way to see which commands are truly accepted by gcc
Is there some other way that could work using cygwin's gcc to compile this main.c example?
Compiling gcc for windows from sources with the proper option could maybe get --unresolved-symbols to work?
My motivation for this whole thing is that I want to unit test a single function from big files, that have multiple functions. Like in the following example:
#include "foobar.h"
int foo(void)
{
return 0;
}
void bar(void)
{
foobar();
}
The declaration of foobar() is in the foobar.h and the definition is in another file called foobar.c
If I wanted to run a unit test, which just links against the symbol foo() I would still get a linker error because of the missing symbol for foobar(). (linking against foobar.o would lead me to link to the complete chain of dependencies, which I want to avoid)
If this --unresolved-symbols option would work, then I would not need to mock or stub the foobar() function in my unit test.
I do understand that there are tools that can create automatically mocks, nevertheless I would like to get this to work.
Thanks for reading through.