Bump package config script version

Author: CodaFi

utils/make-pkgconfig.swift

@@ -63,7 +63,7 @@ func makeFile() throws {
   }
 
   /// Ensure we have llvm-config in the PATH
-  guard let llvmConfig = which("llvm-config-3.9") ?? which("llvm-config") ?? brewLLVMConfig() else {
+  guard let llvmConfig = which("llvm-config-6.0") ?? which("llvm-config") ?? brewLLVMConfig() else {
     throw "Failed to find llvm-config. Ensure llvm-config is installed and " +
           "in your PATH"
   }
@@ -84,8 +84,8 @@ func makeFile() throws {
 
   let version = (components[0], components[1], components[2])
 
-  guard version > (3, 9, 0) else {
-    throw "LLVMSwift requires LLVM version >=3.9.0, but you have \(versionStr)"
+  guard version >= (6, 0, 0) else {
+    throw "LLVMSwift requires LLVM version >=6.0.0, but you have \(versionStr)"
   }
 
   print("LLVM version is \(versionStr)")