Test: Fix copy-pasta in spi_helper.swift by making SPIStruct type a struct instead of a class.

Author: tshortli

test/SPI/Inputs/spi_helper.swift

@@ -13,7 +13,7 @@ public func genericFunc<T>(_ t: T) { print(t) }
 
 @_spi(HelperSPI) public func spiFunc() { print("spiFunc") }
 
-@_spi(HelperSPI) public class SPIStruct {
+@_spi(HelperSPI) public struct SPIStruct {
   @_spi(HelperSPI) public init() { print("SPIStruct.init") }
   @_spi(HelperSPI) public func spiMethod() { print("SPIStruct.spiMethod") }
   @_spi(HelperSPI) public var spiVar = "text"

test/SPI/spi_client.swift

@@ -28,7 +28,7 @@ c.spiMethod()
 c.spiVar = "write"
 print(c.spiVar)
 
-let s = SPIStruct()
+var s = SPIStruct()
 s.spiMethod()
 s.spiInherit()
 s.spiDontInherit() // expected-error {{'spiDontInherit' is inaccessible due to '@_spi' protection level}}

test/SPI/spi_symbols.swift

@@ -8,7 +8,7 @@
 
 // Look for the SPI symbols in the IR
 // CHECK-IR: define swiftcc void @"$s10spi_helper0A4FuncyyF"
-// CHECK-IR: define swiftcc void @"$s10spi_helper9SPIStructC0A6MethodyyF"
+// CHECK-IR: define swiftcc void @"$s10spi_helper9SPIStructV0A6MethodyyF"
 // CHECK-IR: define swiftcc void @"$s10spi_helper8SPIClassC0A6MethodyyF"
 // CHECK-IR: define swiftcc void @"$s10spi_helper7SPIEnumO0A6MethodyyF"
 // CHECK-IR: define swiftcc void @"$s10spi_helper12PublicStructV0A6MethodyyF"
@@ -22,4 +22,4 @@
 // CHECK-TBD: _$s10spi_helper12otherApiFuncyyF
 // CHECK-TBD: _$s10spi_helper7SPIEnumO0A6MethodyyF
 // CHECK-TBD: _$s10spi_helper8SPIClassC0A6MethodyyF
-// CHECK-TBD: _$s10spi_helper9SPIStructC0A6MethodyyF
+// CHECK-TBD: _$s10spi_helper9SPIStructV0A6MethodyyF