Allow linker flags to pass through to wasm-ld by default.

[sbc100]

Rather then maintain an ever growing whitelist of supported linker
flags, instead list the linker flags that we want to explicitly ignore
for compatibility purposed with existing build systems.

[kripken]

Seems reasonable to me, but we've gone back and forth on this and I don't have a deep understanding of real-world linker usage, so it does worry me.

cc @Beuc and @Brion who have large real-world build systems that it might be good to verify work with this.

[kripken]

I guess this code was just moved around, but maybe this should integrate with the warning manager?

[sbc100]

I'll do that as part of the outstanding warning manager changes.

[sbc100]

I imagine there will be more linker flags we need to add to this list, but it should be a finite about of work to get them added.

[Beuc]

At first glance I'm not sure of the impact.
RenPyWeb's build system is fully automated (emsdk_env.sh && make, basically), fully static too, you can check https://github.com/renpy/renpyweb

[sbc100]

I seem to be getting unrelated build errors when trying to build renpyweb:

simd_none.lo  
../wrjpgcom.c:449:13: error: implicitly declaring library function 'strlen' with type 'unsigned long (const char *)'
      [-Werror,-Wimplicit-function-declaration]
        if (strlen(argv[argn]) + 2 >= (size_t) MAX_COM_LENGTH) {
            ^
../wrjpgcom.c:449:13: note: include the header <string.h> or explicitly provide a declaration for 'strlen'
../wrjpgcom.c:454:9: error: implicitly declaring library function 'strcpy' with type 'char *(char *, const char *)'
      [-Werror,-Wimplicit-function-declaration]
        strcpy(comment_arg, argv[argn]+1);
        ^
../wrjpgcom.c:454:9: note: include the header <string.h> or explicitly provide a declaration for 'strcpy'
../wrjpgcom.c:469:11: error: implicitly declaring library function 'strcat' with type 'char *(char *, const char *)'
      [-Werror,-Wimplicit-function-declaration]
          strcat(comment_arg, " ");
          ^

Seems to be releated to the NEED_BSD_STRINGS configure setting? .. but its unrelated to this change since I'm building with master still.

[Beuc]

This patch seems to depend on others (since 1.39.11), it doesn't apply cleanly and I can't test, but for the record here's a matching log excerpt of ./scripts/libjpeg-turbo.sh in 1.39.11:

/bin/bash ./libtool --mode=link --tag=CC renpyweb/emsdk/upstream/emscripten/emcc  -O3   -o wrjpgcom  wrjpgcom.o libjpeg.la 
shared:WARNING: Assuming object file output in the absence of `-c`, based on output filename. Please add with `-c` or `-r` to avoid this warning
/bin/bash ./libtool --mode=link --tag=CC renpyweb/emsdk/upstream/emscripten/emcc  -O3   -o jcstest  jcstest.o libjpeg.la 
renpyweb/emsdk/upstream/emscripten/emcc -O3 -o wrjpgcom wrjpgcom.o  ./.libs/libjpeg.a
renpyweb/emsdk/upstream/emscripten/emcc -O3 -o jcstest jcstest.o  ./.libs/libjpeg.a

[sbc100]

I'd like to go ahead and land this, and then add the blacklist as we get reports from the wild about flags that people want to be able to use (but are not supported by wasm-ld).