CDRIVER-4234 Detect arc4random_buf using cmake

[ryandesign]

Detect the availability of arc4random_buf when running cmake rather than using a hardcoded list of platforms on which it is available. Fixes build failure on Mac OS X 10.6 where it is not available.

Also now make arc4random_buf the first choice to use if it is available. Previously, if rand_r was not available, the older rand would be used even if arc4random_buf was available.

[kevinAlbs]

LGTM, thank you for the contribution @ryandesign!

[muzuiget]

This issue also happen in macOS 11

[ryandesign]

@muzuiget Which issue are you referring to? The code should have already built fine on Mac OS X 10.7 and later, including macOS 11 and 12; it did for me. This PR was specifically to fix Mac OS X 10.6 and earlier which don't have arc4random_buf.

[muzuiget]

@ryandesign I built v1.20.0 fail on macOS 11, it report a arc4random_buf error. It looks like this PR should fix this issue.

[ryandesign]

It may, but arc4random_buf exists on 10.7 and later, so if your machine is reporting that it doesn't, there is something else wrong.

[muzuiget]

@ryandesign

I built it on Azure Pipelines macOS-11 image, it was success in v1.19.1, but fail in v1.20.0. I just update the version number, the build script didn't changed.

The build script:

VERSION=1.20.0
URL=https://github.com/mongodb/mongo-c-driver/releases/download/$VERSION/mongo-c-driver-$VERSION.tar.gz
mkdir mongo-c-driver
cd mongo-c-driver
wget -q $URL -O - | tar xz --strip-components=1
mkdir out
cd out
cmake \
    -DCMAKE_INSTALL_PREFIX="$OUTPUT_DIR" \
    -DCMAKE_BUILD_TYPE=Release \
    -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF \
    -DENABLE_MONGOC=OFF \
    ..
cmake --build . --config Release --target install

The build log:

+ cmake --build . --config Release --target install
[  1%] Building C object src/libbson/CMakeFiles/bson_shared.dir/src/bson/bcon.c.o
[  2%] Building C object src/libbson/CMakeFiles/bson_shared.dir/src/bson/bson.c.o
[  4%] Building C object src/libbson/CMakeFiles/bson_shared.dir/src/bson/bson-atomic.c.o
[  5%] Building C object src/libbson/CMakeFiles/bson_shared.dir/src/bson/bson-clock.c.o
[  7%] Building C object src/libbson/CMakeFiles/bson_shared.dir/src/bson/bson-context.c.o
/Users/runner/work/1/s/build/mongo-c-driver/src/libbson/src/bson/bson-context.c:234:4: error: implicit declaration of function 'arc4random_buf' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
   arc4random_buf (&result, sizeof (result));
   ^
1 error generated.
make[2]: *** [src/libbson/CMakeFiles/bson_shared.dir/src/bson/bson-context.c.o] Error 1
make[1]: *** [src/libbson/CMakeFiles/bson_shared.dir/all] Error 2
make: *** [all] Error 2
##[error]Bash exited with code '2'.

Or maybe Azure Pipelines has update the macOS-11 image, but I don't know what cause this error.

[muzuiget]

Here is more details the macOS-11 image in build log:

Virtual Environment
Environment: macos-11
Version: 20211207.1
Included Software: https://github.com/actions/virtual-environments/blob/macOS-11/20211207.1/images/macos/macos-11-Readme.md
Image Release: https://github.com/actions/virtual-environments/releases/tag/macOS-11%2F20211207.1

[kevinAlbs]

@muzuiget / @ryandesign, the error on macOS 11 may be caused by CDRIVER-4233. There is a proposed fix in #910.

[ryandesign]

Ohh right, I forgot about that already.