[Emscripten] "Legalize cannot Expand SINT_TO_FP for i64 yet" failure with buildbot

In reference to https://github.com/libretro/FBNeo/issues/938, the current emscripten buildbot can't handle the FBNeo core.

It fails to build with the following error :

clang-10: /b/s/w/ir/cache/builder/emscripten-releases/llvm-project/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:2418: llvm::SDValue (anonymous namespace)::SelectionDAGLegalize::ExpandLegalINT_TO_FP(llvm::SDNode *, llvm::SDValue &): Assertion `!isSigned && "Legalize cannot Expand SINT_TO_FP for i64 yet"' failed.
Stack dump:
0.	Program arguments: /opt/emsdk/upstream/bin/clang-10 -cc1 -triple wasm32-unknown-emscripten -emit-obj -disable-free -main-file-name pokey.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=none -menable-no-infs -menable-no-nans -menable-unsafe-fp-math -fno-signed-zeros -mreassociate -freciprocal-math -ffp-contract=fast -frounding-math -ffinite-math-only -masm-verbose -mconstructor-aliases -target-cpu generic -fvisibility hidden -dwarf-column-info -debugger-tuning=gdb -resource-dir /opt/emsdk/upstream/lib/clang/10.0.0 -D __EMSCRIPTEN_major__=1 -D __EMSCRIPTEN_minor__=39 -D __EMSCRIPTEN_tiny__=5 -D _LIBCPP_ABI_VERSION=2 -D unix -D __unix -D __unix__ -D GIT_VERSION=" 1c93f8a" -D NDEBUG -D EXTERNAL_ZLIB -D INCLUDE_7Z_SUPPORT -D _7ZIP_PPMD_SUPPPORT -D _7ZIP_ST -D __LIBRETRO__ -D NO_VIZ -D _LARGEFILE64_SOURCE=0 -D _FILE_OFFSET_BITS=32 -D LSB_FIRST -D USE_SPEEDHACKS -I ../../burner/win32 -I ../../burner/libretro/libretro-common/include -I ../../burner/libretro -I ../../burn -I ../../cpu -I ../../burn/snd -I ../../burn/devices -I ../../intf -I ../../intf/input -I ../../intf/cd -I ../../intf/audio -I ../../burner -I ../../cpu -I ../../cpu/f8 -I ../../cpu/i8039 -I ../../cpu/i8051 -I ../../cpu/i8x41 -I ../../cpu/m377 -I ../../cpu/m6805 -I ../../cpu/tlcs900 -I ../../cpu/tms32010 -I ../../cpu/upd7725 -I ../../cpu/upd7810 -I ../../cpu/v60 -I ../../cpu/z80 -I ../../cpu/z180 -I ../../dep/libs/zlib -I ../../dep/libs/lib7z -I ../../burn/drv/capcom -I ../../burn/drv/konami -I ../../burn/drv/dataeast -I ../../burn/drv/cave -I ../../burn/drv/neogeo -I ../../burn/drv/psikyo -I ../../burn/drv/sega -I ../../burn/drv/toaplan -I ../../burn/drv/taito -I ../../burn/drv/irem -I ../../burn/drv/pce -I ../../dep/generated -I ../../dep/libs -I ../../burner/libretro/deps/ugui -D EMSCRIPTEN -internal-isystem /include/wasm32-emscripten/c++/v1 -internal-isystem /include/c++/v1 -internal-isystem /opt/emsdk/upstream/lib/clang/10.0.0/include -internal-isystem /include/wasm32-emscripten -internal-isystem /include -O3 -Werror=implicit-function-declaration -Wall -W -Wshadow -Wno-long-long -Wno-write-strings -Wunknown-pragmas -Wundef -Wno-conversion -Wno-missing-braces -Wno-multichar -Wuninitialized -Wpointer-arith -Wno-inline -Wno-unused-value -Wno-sequence-point -Wno-extra -Wno-strict-aliasing -Wno-write-strings -Wno-address -Wno-unused-but-set-variable -Wno-narrowing -Wno-pedantic -pedantic -std=gnu++98 -fdeprecated-macro -fdebug-compilation-dir /builds/libretro/FBNeo/src/burner/libretro -ferror-limit 19 -fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gnustep -fcxx-exceptions -fexceptions -fno-common -fdiagnostics-show-option -vectorize-loops -vectorize-slp -nostdsysteminc -isystem/opt/emsdk/upstream/emscripten/system/include/libcxx -isystem/opt/emsdk/upstream/emscripten/system/lib/libcxxabi/include -isystem/opt/emsdk/upstream/emscripten/system/include/compat -isystem/opt/emsdk/upstream/emscripten/system/include -isystem/opt/emsdk/upstream/emscripten/system/include/libc -isystem/opt/emsdk/upstream/emscripten/system/lib/libc/musl/arch/emscripten -isystem/opt/emsdk/upstream/emscripten/system/local/include -isystem/builds/libretro/FBNeo/.cache/emscripten/wasm-obj/include -isystem/opt/emsdk/upstream/emscripten/system/include/SDL -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr -o ../../burn/snd/pokey.o -x c++ ../../burn/snd/pokey.cpp 
1.	<eof> parser at end of file
2.	Code generation
3.	Running pass 'Function Pass Manager' on module '../../burn/snd/pokey.cpp'.
4.	Running pass 'WebAssembly Instruction Selection' on function '@_Z16pokey_register_rii'

I saw some references to that "Legalize cannot Expand SINT_TO_FP for i64 yet" failed assertion on internet, it seems to be a common issue with clang-10 and some targets, and upgrading to clang-11 has apparently fixed this issue for those targets.

Switching to the latest emscripten sdk (clang-14 based ?) was tested this week, it fixed the build but broke the runtime for all of emscripten retroarch, so for now it was reverted to clang-10 and FBNeo was removed from that buildbot

Start by reproducing the Emscripten build failure while compiling burn/snd/pokey.cpp with the clang-10-based SDK described in the stack trace. Compare the latest Emscripten SDK as a possible direction, then verify both that the FBNeo build succeeds and that the change does not reproduce the reported runtime breakage across Emscripten RetroArch.