Emit 'fneg' for unary minus with floating point operand.

Simple negation from 0 doesn't work in case -0.0 argument.

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/CodeGenerator.kt

@@ -588,6 +588,7 @@ internal class FunctionGenerationContext(val function: LLVMValueRef,
 
     fun fsub(arg0: LLVMValueRef, arg1: LLVMValueRef, name: String = ""): LLVMValueRef = LLVMBuildFSub(builder, arg0, arg1, name)!!
     fun fadd(arg0: LLVMValueRef, arg1: LLVMValueRef, name: String = ""): LLVMValueRef = LLVMBuildFAdd(builder, arg0, arg1, name)!!
+    fun fneg(arg: LLVMValueRef, name: String = ""): LLVMValueRef = LLVMBuildFNeg(builder, arg, name)!!
 
     fun select(ifValue: LLVMValueRef, thenValue: LLVMValueRef, elseValue: LLVMValueRef, name: String = ""): LLVMValueRef =
             LLVMBuildSelect(builder, ifValue, thenValue, elseValue, name)!!

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/IntrinsicGenerator.kt

@@ -699,10 +699,10 @@ internal class IntrinsicGenerator(private val environment: IntrinsicGeneratorEnv
     private fun FunctionGenerationContext.emitUnaryMinus(args: List<LLVMValueRef>): LLVMValueRef {
         val first = args[0]
         val destTy = first.type
-        val const0 = makeConstOfType(destTy, 0)
         return if (destTy.isFloatingPoint()) {
-            fsub(const0, first)
+            fneg(first)
         } else {
+            val const0 = makeConstOfType(destTy, 0)
             sub(const0, first)
         }
     }