Meta: Add the start of a gn build based on the LLVM gn build

"based on" in this context means "largely copied from"

Meta/gn/secondary/Userland/Libraries/LibCrypt/BUILD.gn

@@ -0,0 +1,36 @@
+group("LibCrypt") {
+  deps = []
+  libs = []
+  if (current_os == "serenity") {
+    deps += [
+      ":crypt_shared",
+      ":crypt_static",
+    ]
+  } else if (current_os == "linux") {
+    libs += [ "crypt" ]
+  }
+}
+
+if (current_os == "serenity") {
+  # FIXME: Special handling for LibCrypo/Hash/SHA2.cpp
+  shared_library("crypt_shared") {
+    output_name = "crypt"
+    cflags_cc = [ "-nostdlib" ]
+    ldflags = [
+      "-nostdlib",
+      "-static-libstdc++",
+    ]
+    sources = [
+      "crypt.cpp",
+      "crypt.h",
+    ]
+  }
+
+  static_library("crypt_static") {
+    output_name = "crypt"
+    sources = [
+      "crypt.cpp",
+      "crypt.h",
+    ]
+  }
+}