[K/N] Fix mingw_x86 compilation

It was broken in 9ed97a27f1.

kotlin-native/konan/konan.properties

@@ -928,7 +928,7 @@ linkerDynamicFlags.mingw_x86 = -shared
 linkerKonanFlags.mingw_x86 = -static-libgcc -static-libstdc++ \
   -Wl,--dynamicbase \
   -Wl,-Bstatic,--whole-archive -lwinpthread -Wl,--no-whole-archive,-Bdynamic \
-  -Wl,--defsym,__cxa_demangle=Konan_cxa_demangle
+  -Wl,--defsym,__cxa_demangle=_Konan_cxa_demangle
 mimallocLinkerDependencies.mingw_x86 = -lbcrypt
 linkerOptimizationFlags.mingw_x86 = -Wl,--gc-sections
 runtimeDefinitions.mingw_x86 = USE_GCC_UNWIND=1 USE_PE_COFF_SYMBOLS=1 KONAN_WINDOWS=1 \

kotlin-native/shared/src/main/kotlin/org/jetbrains/kotlin/konan/target/Linker.kt

@@ -480,11 +480,16 @@ class MingwLinker(targetProperties: MingwConfigurables)
         if (HostManager.hostIsMingw) {
             lldCompatibilityChecker?.let { checkLldCompatibiity ->
                 // -### flag allows to avoid actual linkage process.
+                val konanCxaDemangleSymbol = when (target) {
+                    KonanTarget.MINGW_X64 -> "Konan_cxa_demangle"
+                    KonanTarget.MINGW_X86 -> "_Konan_cxa_demangle"
+                    else -> error("Unexpected target: $target")
+                }
                 val lldCommand = Command(linker).constructLinkerArguments(
                         // Add -fuse-ld to the end of the list to override previous appearances.
                         additionalArguments = listOf("-fuse-ld=$absoluteLldLocation", "-Wl,-###"),
                         // LLD doesn't support defsym.
-                        skipDefaultArguments = listOf("-Wl,--defsym,__cxa_demangle=Konan_cxa_demangle")
+                        skipDefaultArguments = listOf("-Wl,--defsym,__cxa_demangle=$konanCxaDemangleSymbol")
                 )
                 checkLldCompatibiity(lldCommand)
             }