Cleanup user-config.jam patch

[guillaumealgis]

• Define the same variables for all targets (iOS, tvOS, macOS)
• Use the right variables for each compiler flag (CXX, LD, etc.)
• Move flags passed to the compiler from build functions to user-config.jam patch to reduce code duplication
  • This will also be needed to easily add support for bcp
• Cleanup variables values dump at beginning of script

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Variables dump before / after

#### Before ```bash BUILD_IOS : YES BUILD_TVOS : YES BUILD_MACOS : YES BOOST_VERSION : 1.72.0 IOS_SDK_VERSION : 13.4 MIN_IOS_VERSION : 11.0 TVOS_SDK_VERSION : 13.4 TVOS_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS13.4.sdk TVOSSIM_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator13.4.sdk MIN_TVOS_VERSION : 11.0 MACOS_SDK_VERSION : 10.15 MACOS_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk MIN_MACOS_VERSION : 10.12 MACOS_ARCHS : x86_64 IOS_ARCHS : arm64 IOS_SIM_ARCHS : x86_64 BOOST_LIBS : atomic chrono date_time exception filesystem program_options random system thread test BOOST_SRC : /Users/guillaume/Apple-Boost-BuildScript/src/boost_1_72_0 IOS_BUILD_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/ios/release/build MACOS_BUILD_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/macos/release/build IOS_FRAMEWORK_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/ios/release/framework MACOS_FRAMEWORK_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/macos/release/framework XCODE_ROOT : /Applications/Xcode-11.4.1.app/Contents/Developer THREADS : -j4 BUILD_VARIANT : release ``` #### After ```bash BOOST_VERSION : 1.72.0 BUILD_IOS : YES IOS_ARCHS : arm64 IOS_SDK_VERSION : 13.4 IOS_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.4.sdk IOSSIM_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator13.4.sdk MIN_IOS_VERSION : 11.0 BUILD_TVOS : YES TVOS_SDK_VERSION : 13.4 TVOS_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS13.4.sdk TVOSSIM_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator13.4.sdk MIN_TVOS_VERSION : 11.0 BUILD_MACOS : YES MACOS_ARCHS : x86_64 MACOS_SDK_VERSION : 10.15 MACOS_SDK_PATH : /Applications/Xcode-11.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk MIN_MACOS_VERSION : 10.12 BOOST_LIBS : atomic chrono date_time exception filesystem program_options random system thread test BOOST_SRC : /Users/guillaume/Apple-Boost-BuildScript/src/boost_1_72_0 XCODE_ROOT : /Applications/Xcode-11.4.1.app/Contents/Developer IOS_BUILD_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/ios/release/build TVOS_BUILD_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/tvos/release/build MACOS_BUILD_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/macos/release/build TVOS_FRAMEWORK_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/tvos/release/framework IOS_FRAMEWORK_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/ios/release/framework MACOS_FRAMEWORK_DIR : /Users/guillaume/Apple-Boost-BuildScript/build/boost/1.72.0/macos/release/framework THREADS : -j4 BUILD_VARIANT : release ```

[faithfracture]

Thanks!