Fix macOS framework builds

[antonc27]

This PR fixes 2 issues with CI builds of macOS framework:

1. Correct flag should be OPUS_BUILD_FRAMEWORK, not BUILD_FRAMEWORK.
2. Correct CMAKE_OSX_ARCHITECTURES should be set, otherwise host arch will be used.

P.S.

2 more thoughts:

1. I haven't checked myself, but iOS framework should also use OPUS_BUILD_FRAMEWORK, not BUILD_FRAMEWORK
2. FRAMEWORK_VERSION in cmake list should be probably set to "A" (major verison), not ${PROJECT_VERSION}