[Fuchsia] Update path to .so in the generated ICD manifest

On Fuchsia the .so files are normally placed in /pkg/lib. Use that path
in the generated ICD manifest file.

Change-Id: Iab7e022f8c74d7de09ac8905e115f4d5cc13ef9a
Bug: chromium:1225002
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/59788
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Commit-Queue: Sergey Ulanov <sergeyu@google.com>
Tested-by: Sergey Ulanov <sergeyu@google.com>

src/Vulkan/BUILD.gn

diff --git a/src/Vulkan/BUILD.gn b/src/Vulkan/BUILD.gn
index dcf48a6..7f4ad97 100644
--- a/src/Vulkan/BUILD.gn
+++ b/src/Vulkan/BUILD.gn
@@ -218,6 +218,8 @@
     library_path = ".\\vk_swiftshader.dll"
   } else if (is_mac) {
     library_path = "./libvk_swiftshader.dylib"
+  } else if (is_fuchsia) {
+    library_path = "/pkg/lib/libvk_swiftshader.so"
   } else {
     library_path = "./libvk_swiftshader.so"
   }