[docs] README: Switch link to clang.llvm.org to use HTTPS.

Author: fcambus

README.md

@@ -16,7 +16,7 @@ files needed to process intermediate representations and convert them into
 object files. Tools include an assembler, disassembler, bitcode analyzer, and
 bitcode optimizer.
 
-C-like languages use the [Clang](http://clang.llvm.org/) frontend. This
+C-like languages use the [Clang](https://clang.llvm.org/) frontend. This
 component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode
 -- and from there into object files, using LLVM.