`llvm-11` changed the default from `-fcommon` to `-fno-common`:
https://reviews.llvm.org/D75056
As a result build fails as:
LD retroarch
duplicate symbol '_apple_platform' in:
obj-unix/release/ui/drivers/ui_cocoa.o
obj-unix/release/ui/drivers/cocoa/cocoa_common.o
duplicate symbol '_apple_platform' in:
obj-unix/release/ui/drivers/ui_cocoa.o
obj-unix/release/gfx/drivers_context/cocoa_gl_ctx.o
ld: 2 duplicate symbols for architecture x86_64
The change moves `apple_platform` definition from `apple_platform.h`
to `cocoa_common.m` leaving only declaration in `apple_platform.h`.
f5ee9e74ba