[vcpkg] fix find_library suffix/prefix definitions for iOS

[derekcyruschow-catapult]

For example, when building dynamic iOS libs for mp3lame, the generated mp3lame-config.cmake would be erroneously looking for libmp3lame.a instead of libmp3lame.dylib.

[dg0yt]

The change is okay IMO. But do you expect this to fix an immediate problem? Sane ports shouldn't depend on this anyways. (It is for portfile script mode. Project mode gets a regular CMake toolchain setup, and so mp3lame-config.cmake will work as expected.)

[derekcyruschow-catapult]

Project mode

The issue I saw was due to a app I have using a vcpkg manifest dependency on mp3lame, which was built via setting the CMake toolchain to use the vcpkg toolchain (<vcpkg-root>/scripts/buildsystems/vcpkg.cmake)...

• this then creates mp3lame-config.cmake;
• which presumably is done in script mode before project mode kicks in to build the app?

https://learn.microsoft.com/en-us/vcpkg/contributing/maintainer-guide

While portfile.cmake's and CMakeLists.txt's share a common syntax and core CMake language constructs (aka "Scripting Commands"), portfiles run in "Script Mode"