Add support for the llvm.is.fpclass instruction

[zlfn]

llvm-cbe does not support Floating-Point Test Intrinsics

Error occurred below while compiling Rust core.

LLVM ERROR: Code generator does not support intrinsic function 'llvm.is.fpclass.f32'!
 #0 0x00005587918d7d72 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /home/zlfn/rust-z80/llvm-project/llvm/lib/Support/Unix/Signals.inc:602:22
 #1 0x00005587918d8143 PrintStackTraceSignalHandler(void*) /home/zlfn/rust-z80/llvm-project/llvm/lib/Support/Unix/Signals.inc:675:1
 #2 0x00005587918d5881 llvm::sys::RunSignalHandlers() /home/zlfn/rust-z80/llvm-project/llvm/lib/Support/Signals.cpp:104:20
 #3 0x00005587918d76cd SignalHandler(int) /home/zlfn/rust-z80/llvm-project/llvm/lib/Support/Unix/Signals.inc:413:1
 #4 0x00007f26779531d0 (/usr/lib/libc.so.6+0x3d1d0)
 #5 0x00007f26779ac3f4 (/usr/lib/libc.so.6+0x963f4)
 #6 0x00007f2677953120 raise (/usr/lib/libc.so.6+0x3d120)
 #7 0x00007f267793a4c3 abort (/usr/lib/libc.so.6+0x244c3)
 #8 0x000055879180f8f3 llvm::report_fatal_error(llvm::Twine const&, bool) /home/zlfn/rust-z80/llvm-project/llvm/lib/Support/ErrorHandling.cpp:125:9
 #9 0x00005587907b286d llvm::IntrinsicLowering::LowerIntrinsicCall(llvm::CallInst*) /home/zlfn/rust-z80/llvm-project/llvm/lib/CodeGen/IntrinsicLowering.cpp:241:33
#10 0x000055879065d30c llvm_cbe::CWriter::lowerIntrinsics(llvm::Function&) /home/zlfn/rust-z80/llvm-project/llvm/projects/llvm-cbe/lib/Target/CBackend/CBackend.cpp:4845:13
#11 0x00005587906455e5 llvm_cbe::CWriter::runOnFunction(llvm::Function&) /home/zlfn/rust-z80/llvm-project/llvm/projects/llvm-cbe/lib/Target/CBackend/CBackend.cpp:249:34
#12 0x000055879106a054 llvm::FPPassManager::runOnFunction(llvm::Function&) /home/zlfn/rust-z80/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1435:20
#13 0x000055879106a326 llvm::FPPassManager::runOnModule(llvm::Module&) /home/zlfn/rust-z80/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1481:13
#14 0x000055879106a772 (anonymous namespace)::MPPassManager::runOnModule(llvm::Module&) /home/zlfn/rust-z80/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1550:20
#15 0x0000558791065448 llvm::legacy::PassManagerImpl::run(llvm::Module&) /home/zlfn/rust-z80/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:535:13
#16 0x000055879106b045 llvm::legacy::PassManager::run(llvm::Module&) /home/zlfn/rust-z80/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1678:1
#17 0x000055878ddbf43c compileModule(char**, llvm::LLVMContext&) /home/zlfn/rust-z80/llvm-project/llvm/projects/llvm-cbe/tools/llvm-cbe/llvm-cbe.cpp:352:12
#18 0x000055878ddbe7cd main /home/zlfn/rust-z80/llvm-project/llvm/projects/llvm-cbe/tools/llvm-cbe/llvm-cbe.cpp:204:35
#19 0x00007f267793be08 (/usr/lib/libc.so.6+0x25e08)
#20 0x00007f267793becc __libc_start_main (/usr/lib/libc.so.6+0x25ecc)
#21 0x000055878ddbdfa5 _start (/home/zlfn/rust-gb/ext/rust-deps/target/avr-unknown-gnu-atmega328/release/deps/../../../../../llvm-cbe+0x922fa5)
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: /home/zlfn/rust-gb/ext/rust-deps/target/avr-unknown-gnu-atmega328/release/deps/../../../../../llvm-cbe core-2ed864bedde1aa0b.ll
1.      Running pass 'Function Pass Manager' on module 'core-2ed864bedde1aa0b.ll'.
2.      Running pass 'C backend' on function '@"_ZN4core3f3221_$LT$impl$u20$f32$GT$7to_bits13ct_f32_to_u3217h321276d7883f215eE"'

[zlfn]

#195
I'm sorry. I didn't see this