Do not use _GNU_SOURCE gratuitously.

[przemoc]

Follow up to previous attempt #1027 that had to be reverted due to not being complete, which was exposed after syncing new stuff from llama.cpp. It uses improvements from ggerganov/llama.cpp#2035 (courtesy of @howard0su).

[przemoc]

Never ending story. We didn't have FreeBSD coverage before in whisper.cpp, so it naturally has to fail now. :)

I whisper.cpp build info: 
I UNAME_S:  FreeBSD
I UNAME_P:  amd64
I UNAME_M:  amd64
I CFLAGS:   -I.              -O3 -DNDEBUG -std=c11   -fPIC -D_XOPEN_SOURCE=600 -pthread -mavx -mavx2 -mfma -mf16c
I CXXFLAGS: -I. -I./examples -O3 -DNDEBUG -std=c++11 -fPIC -D_XOPEN_SOURCE=600 -pthread
I LDFLAGS:  
I CC:       FreeBSD clang version 14.0.5 (https://github.com/llvm/llvm-project.git llvmorg-14.0.5-0-gc12386ae247c)
I CXX:      FreeBSD clang version 14.0.5 (https://github.com/llvm/llvm-project.git llvmorg-14.0.5-0-gc12386ae247c)

cc  -I.              -O3 -DNDEBUG -std=c11   -fPIC -D_XOPEN_SOURCE=600 -pthread -mavx -mavx2 -mfma -mf16c   -c ggml.c -o ggml.o
ggml.c:16438:43: warning: implicit declaration of function 'alloca' is invalid in C99 [-Wimplicit-function-declaration]
    struct ggml_compute_state * workers = alloca(sizeof(struct ggml_compute_state)*n_threads);
                                          ^
ggml.c:16438:33: warning: incompatible integer to pointer conversion initializing 'struct ggml_compute_state *' with an expression of type 'int' [-Wint-conversion]
    struct ggml_compute_state * workers = alloca(sizeof(struct ggml_compute_state)*n_threads);
                                ^         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ggml.c:18[321](https://github.com/ggerganov/whisper.cpp/actions/runs/5621134985/job/15231380392?pr=1129#step:3:324):65: warning: implicit declaration of function 'alloca' is invalid in C99 [-Wimplicit-function-declaration]
    struct ggml_opt_context * opt = (struct ggml_opt_context *) alloca(sizeof(struct ggml_opt_context));
                                                                ^
ggml.c:18321:37: warning: cast to 'struct ggml_opt_context *' from smaller integer type 'int' [-Wint-to-pointer-cast]
    struct ggml_opt_context * opt = (struct ggml_opt_context *) alloca(sizeof(struct ggml_opt_context));
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4 warnings generated.
c++ -I. -I./examples -O3 -DNDEBUG -std=c++11 -fPIC -D_XOPEN_SOURCE=600 -pthread -c whisper.cpp -o whisper.o
c++ -I. -I./examples -O3 -DNDEBUG -std=c++11 -fPIC -D_XOPEN_SOURCE=600 -pthread examples/main/main.cpp examples/common.cpp examples/common-ggml.cpp ggml.o whisper.o -o main 
ld: error: undefined symbol: alloca
>>> referenced by ggml.c
>>>               ggml.o:(ggml_graph_compute)
>>> referenced by ggml.c
>>>               ggml.o:(ggml_opt)
>>> did you mean: allocm
>>> defined in: /lib/libc.so.7
c++: error: linker command failed with exit code 1 (use -v to see invocation)
gmake: *** [Makefile:285: main] Error 1

[przemoc]

alloca() function (FreeBSD man page, Linux man page) is not the best thing to use, but I don't want to refactor stuff in this PR. Will need to dig into this more to understand why it fails now, but it may or may not be today, as I mostly used my quota for side things today. :)

Maybe with minimal FTMs we're adding FreeBSD limits availability of non-POSIX interfaces. Or something like that.

I may need to set up FreeBSD VM to play with it more, maybe during weekend. Haven't touched FreeBSD in many years.

[przemoc]

By looking at headers only:
https://github.com/freebsd/freebsd-src/blob/release/13.2.0/include/stdlib.h#L245-L259
https://github.com/freebsd/freebsd-src/blob/release/13.2.0/sys/sys/cdefs.h#L694-L766
it seems that alloca() is available in FreeBSD only when __BSD_VISIBLE is set to 1. I don't see any cleaner way than adding it explicitly for FreeBSD, as normally __BSD_VISIBLE seems to be set to 1 only when no standard-related FTMs are used at all.

So I looked at other popular BSD headers too.

For OpenBSD
https://github.com/openbsd/src/blob/e03a31515fc3008507a9ab3997d0ac6226da8bb6/include/stdlib.h#L266-L267
https://github.com/openbsd/src/blob/e03a31515fc3008507a9ab3997d0ac6226da8bb6/sys/sys/cdefs.h#L387-L411
it seems that _BSD_SOURCE should do the job, which looks like a cleaner solution. Just setting __BSD_VISIBLE to 1 would be changed to 0 in the presence of __POSIX_VISIBLE that is set due to FTM we use, so _BSD_SOURCE is better approach. (No, FreeBSD does not recognize _BSD_SOURCE.)

And for NetBSD
https://github.com/NetBSD/src/blob/ab3fdd40bbfe9c973ebe532869b675339861eb30/include/stdlib.h#L271-L276
_NETBSD_SOURCE seems to be what is needed.

I'll have to add all this to Makefile and CMakeLists.txt with appropriate comments, so that it could be most likely removed if/when alloca() will be gone from ggml.c (and examples that use it, presently only in llama.cpp).

EDIT:
For DragonFlyBSD
https://github.com/DragonFlyBSD/DragonFlyBSD/blob/v6.4.0/include/stdlib.h#L248-L263
https://github.com/DragonFlyBSD/DragonFlyBSD/blob/v6.4.0/sys/sys/cdefs.h#L654-L715
situation is analogous like in FreeBSD.

[przemoc]

Before updating this PR, I will create yet another PR to simply add support for building on DragonFlyBSD/NetBSD/OpenBSD, then I will rebase this one on top of that with new BSD-related refinements.

[przemoc]

@ggerganov, when you'll have some spare time for whisper.cpp (as a break from llama.cpp, I guess :>), it would be great if you could merge my recent PRs: #1210, #1211, #1212. It will help continuing working on and rebasing current PR (#1129).

[przemoc]

BTW There should be no issues with merging #1238 first and then this #1129.

[ggerganov]

Will look to merge this after the sync: #1247

[przemoc]

I saw that #1247 got merged.
I rebased the branch, but it's kind of untested locally yet, so theoretically it may be not clean.

[przemoc]

Portable applications should employ sysconf(_SC_PAGESIZE) instead of getpagesize(), so I will create separate PR for llama.cpp and whisper.cpp to do that, to be merged before this PR will be merged. But tbh, it's unclear to me if macOS supports sysconf(_SC_PAGESIZE) (as I don't see it in apple-oss-distributions/xnu, but maybe that's wrong place to look at). I guess checks will tell us the truth...

[przemoc]

#1251 has been created.

[przemoc]

Rebased after #1251 got merged.

[ggerganov]

Thank you for the effort @przemoc !

[przemoc]

You're welcome!
Hopefully we won't have new issues (not covered by checks) due to this change.