Vulkan: Fix ICD function exports.

This change is needed to ensure that vk_icdXXX entry points
are exported, as expected by Khronos' Vulkan loader.

Change-Id: I25b232eb3a99767072be198621bda91e3f9f9cbe
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/33050
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: David Turner <digit@google.com>
Presubmit-Ready: David Turner <digit@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

src/Vulkan/libVulkan.cpp

diff --git a/src/Vulkan/libVulkan.cpp b/src/Vulkan/libVulkan.cpp
index ef70b3f..dbd2644 100644
--- a/src/Vulkan/libVulkan.cpp
+++ b/src/Vulkan/libVulkan.cpp
@@ -113,14 +113,14 @@
 
 extern "C"
 {
-VKAPI_ATTR PFN_vkVoidFunction VKAPI_CALL vk_icdGetInstanceProcAddr(VkInstance instance, const char* pName)
+VK_EXPORT VKAPI_ATTR PFN_vkVoidFunction VKAPI_CALL vk_icdGetInstanceProcAddr(VkInstance instance, const char* pName)
 {
 	TRACE("(VkInstance instance = %p, const char* pName = %p)", instance, pName);
 
 	return vk::GetInstanceProcAddr(vk::Cast(instance), pName);
 }
 
-VKAPI_ATTR VkResult VKAPI_CALL vk_icdNegotiateLoaderICDInterfaceVersion(uint32_t* pSupportedVersion)
+VK_EXPORT VKAPI_ATTR VkResult VKAPI_CALL vk_icdNegotiateLoaderICDInterfaceVersion(uint32_t* pSupportedVersion)
 {
 	*pSupportedVersion = 3;
 	return VK_SUCCESS;