[unification] Move //zircon/system/ulib/blktest to the GN build

Affected libraries:
//zircon/system/ulib/blktest

scripts/unification/verify_element_move.py --reference local/initial.json:

Error     aux         element removed: lib/asan-ubsan/libblktest.so
Error     aux         element removed: lib/ubsan-sancov-full/libblktest.so
Error     aux         element removed: lib/ubsan/libblktest.so
Error     aux         element removed: lib/profile/libblktest.so
Error     aux         element removed: lib/libblktest.so
Error     aux         element removed: lib/asan/libblktest.so
Error     aux         element removed: lib/sancov/libblktest.so
Error     aux         element removed: lib/ubsan-sancov/libblktest.so
Error     image       size change for lib/libblktest.so: +6% (93.5K)
Error: summaries do not match!

Generated with //scripts/unification/move_cpp_library.py

Bug: 36548
Change-Id: I432c8cecafc93cd65e8996c5117f4f9ec4086bfe
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/378135
Reviewed-by: P.Y. Laligand <pylaligand@google.com>
Commit-Queue: Theodore Dubois <tbodt@google.com>
diff --git a/build/unification/images/BUILD.gn b/build/unification/images/BUILD.gn
index 9b8594d..18eabe11 100644
--- a/build/unification/images/BUILD.gn
+++ b/build/unification/images/BUILD.gn
@@ -617,7 +617,6 @@
     "backtrace",
 #------------------
 #------------------
-    "blktest",
 #------------------
 #------------------
     "devmgr-integration-test",
diff --git a/src/devices/block/bin/blktest/BUILD.gn b/src/devices/block/bin/blktest/BUILD.gn
index 34a431f..eac3c22 100644
--- a/src/devices/block/bin/blktest/BUILD.gn
+++ b/src/devices/block/bin/blktest/BUILD.gn
@@ -18,13 +18,14 @@
   if (is_fuchsia) {
     configs += [ "//build/unification/config:zircon-migrated" ]
   }
+
   # Dependent manifests unfortunately cannot be marked as `testonly`.
   # TODO(44278): Remove when converting this file to proper GN build idioms.
   testonly = false
   sources = [ "main.c" ]
   deps = [
-    "//zircon/public/lib/blktest",
     "//zircon/public/lib/unittest",
+    "//zircon/system/ulib/blktest",
   ]
 }
 
diff --git a/zircon/system/ulib/BUILD.gn b/zircon/system/ulib/BUILD.gn
index c281073..2660f96 100644
--- a/zircon/system/ulib/BUILD.gn
+++ b/zircon/system/ulib/BUILD.gn
@@ -68,7 +68,6 @@
     "bitmap",
 #------------------
 #------------------
-    "blktest",
 #------------------
 #------------------
     "blobfs",
diff --git a/zircon/system/ulib/blktest/BUILD.gn b/zircon/system/ulib/blktest/BUILD.gn
index 0203ab3..25826be 100644
--- a/zircon/system/ulib/blktest/BUILD.gn
+++ b/zircon/system/ulib/blktest/BUILD.gn
@@ -2,6 +2,18 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+##########################################
+# Though under //zircon, this build file #
+# is meant to be used in the Fuchsia GN  #
+# build.                                 #
+# See fxb/36548.                         #
+##########################################
+
+assert(!defined(zx) || zx != "/",
+       "This file can only be used in the Fuchsia GN build.")
+
+import("//build/unification/zx_library.gni")
+
 zx_library("blktest") {
   sdk = "shared"
   sdk_headers = [ "blktest/blktest.h" ]
@@ -9,17 +21,16 @@
   testonly = true
   sources = [ "blktest.cc" ]
   deps = [
-    "$zx/system/fidl/fuchsia-hardware-block:c",
-    "$zx/system/ulib/block-client",
-    "$zx/system/ulib/fbl",
-    "$zx/system/ulib/fdio",
-    "$zx/system/ulib/fdio-caller",
-    "$zx/system/ulib/fzl",
-    "$zx/system/ulib/pretty",
-    "$zx/system/ulib/sync",
-    "$zx/system/ulib/unittest",
-    "$zx/system/ulib/zircon",
-    "$zx/system/ulib/zx",
+    "//zircon/public/lib/block-client",
+    "//zircon/public/lib/fbl",
+    "//zircon/public/lib/fdio",
+    "//zircon/public/lib/fdio-caller",
+    "//zircon/public/lib/fzl",
+    "//zircon/public/lib/pretty",
+    "//zircon/public/lib/sync",
+    "//zircon/public/lib/unittest",
+    "//zircon/public/lib/zx",
+    "//zircon/system/fidl/fuchsia-hardware-block:c",
   ]
-  configs += [ "$zx_build/public/gn/config:static-libc++" ]
+  configs += [ "//build/config/fuchsia:static_cpp_standard_library" ]
 }