Android cross-compile on macOS: Fix for compile error addressed Float80 data type.

[vgorloff]

Swift forum discussion: https://forums.swift.org/t/android-crosscompilation-on-macos-is-swift-float80-support-really-needed-for-android-intel-x86-and-x86-64-targets/25835

This PR disables Float80 support for Android. This PR fixes compile error shown below:

cd /swift-everywhere-toolchain/ToolChain/Build/darwin/swift && ninja -j3 swiftGlibc-android-i686 swiftCore-android-i686 swiftSwiftOnoneSupport-android-i686
[33/75] Building CXX object stdlib/public/runtime/CMakeFiles/swiftRuntime-android-i686.dir/SwiftDtoa.cpp.o
FAILED: stdlib/public/runtime/CMakeFiles/swiftRuntime-android-i686.dir/SwiftDtoa.cpp.o
/swift-everywhere-toolchain/ToolChain/Build/darwin/llvm/./bin/clang++  \
-DCMARK_STATIC_DEFINE -DGTEST_HAS_RTTI=0 -D_DEBUG -D__STDC_CONSTANT_MACROS \
-D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Istdlib/public/runtime \
-I/swift-everywhere-toolchain/ToolChain/Sources/swift/stdlib/public/runtime \
-Iinclude -I/swift-everywhere-toolchain/ToolChain/Sources/swift/include \
-I/swift-everywhere-toolchain/ToolChain/Sources/llvm/include \
-I/swift-everywhere-toolchain/ToolChain/Build/darwin/llvm/include \
-I/swift-everywhere-toolchain/ToolChain/Sources/llvm/tools/clang/include \
-I/swift-everywhere-toolchain/ToolChain/Build/darwin/llvm/tools/clang/include \
-I/swift-everywhere-toolchain/ToolChain/Sources/cmark/src \
-I/swift-everywhere-toolchain/ToolChain/Build/darwin/cmark/src \
-Wno-unknown-warning-option -Werror=unguarded-availability-new -fno-stack-protector \
-fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -std=c++11 -Wall -Wextra -Wno-unused-parameter \
-Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-class-memaccess \
-Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fdiagnostics-color -Werror=switch -Wdocumentation \
-Wimplicit-fallthrough -Wunreachable-code -Woverloaded-virtual -DOBJC_OLD_DISPATCH_PROTOTYPES=0 \
-fno-sanitize=all -DLLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING=1 -O3  \
-isysroot /Volumes/Data/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk   \
-UNDEBUG  -fno-exceptions -fno-rtti -Wall -Wglobal-constructors -Wexit-time-destructors -fvisibility=hidden -DswiftCore_EXPORTS \
-I/swift-everywhere-toolchain/ToolChain/Sources/swift/include -DSWIFT_TARGET_LIBRARY_NAME=swiftRuntime \
-target i686-unknown-linux-android \
--sysroot=/Users/vova/Library/Android/sdk/ndk-bundle/platforms/android-24/arch-x86 \
-B /Users/vova/Library/Android/sdk/ndk-bundle/toolchains/x86-4.9/prebuilt/darwin-x86_64/i686-linux-android/bin \
-O2 -momit-leaf-frame-pointer -g0 -DNDEBUG "-I/ndk-bundle/sources/cxx-stl/llvm-libc++/include" \
/ndk-bundle/sysroot/usr/include/i686-linux-android" -D__ANDROID_API__=24 \
-isystem /swift-everywhere-toolchain/ToolChain/Sources/icu/icu4c/source/common \
-isystem /swift-everywhere-toolchain/ToolChain/Sources/icu/icu4c/source/i18n \
-MD -MT stdlib/public/runtime/CMakeFiles/swiftRuntime-android-i686.dir/SwiftDtoa.cpp.o \
-MF stdlib/public/runtime/CMakeFiles/swiftRuntime-android-i686.dir/SwiftDtoa.cpp.o.d \
-o stdlib/public/runtime/CMakeFiles/swiftRuntime-android-i686.dir/SwiftDtoa.cpp.o \
-c /swift-everywhere-toolchain/ToolChain/Sources/swift/stdlib/public/runtime/SwiftDtoa.cpp
/swift-everywhere-toolchain/ToolChain/Sources/swift/stdlib/public/runtime/SwiftDtoa.cpp:148:2: error: "Are you certain `long double` on this platform is really Intel 80-bit extended precision?"

#error "Are you certain `long double` on this platform is really Intel 80-bit extended precision?"
 ^
1 error generated.

[compnerd]

CC: @stephentyrone

[compnerd]

@swift-ci please smoke test

[finagolfin]

Note that @stephentyrone is wrong in that thread when he says "it appears to me that long double on Android is just an alias of double, even on x86." It may seem that way on 32-bit Android platforms, where double and long double are both 64-bit, even on x86, but on 64-bit Android, long double is 128-bit, even on x86_64.

[drodriguez]

Thanks!

I have started support for Float128 for Android AArch64, but I hit a couple road blocks, and I never finished. I think the only code I uploaded was https://github.com/drodriguez/swift/tree/integers-128 which is needed for some return value of Float128. I have some commit or stash with work for the actual Float128 locally. I will see if I can find it, and upload it, so maybe someone can work on it.

[drodriguez]

@swift-ci please smoke test

[vgorloff]

Looks like we can merge this PR.
Thank you!

[stephentyrone]

Note that @stephentyrone is wrong in that thread when he says "it appears to me that long double on Android is just an alias of double, even on x86." It may seem that way on 32-bit Android platforms, where double and long double are both 64-bit, even on x86, but on 64-bit Android, long double is 128-bit, even on x86_64.

That is a spectacularly bad choice, but I suppose they'll get to learn why in the fullness of time, and the reasons why it's a bad idea fortunately don't really impact Swift. In any event, it doesn't change the basic correctness of this patch; if/when the stdlib vends a Float128 type, we can import long double as that on Android and arm64 Linux.

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 484bae6

[vgorloff]

Seems like CI trying to build non-existing branch and this cause build failure :0