[Branch-Rename] Fix some links

According to the [[ https://foundation.llvm.org/docs/branch-rename/ | status of branch rename ]], the master branch of the LLVM repository is removed on 28 Jan 2021.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D95766
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index ba5170c..6dc488e 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -5242,7 +5242,7 @@
 
   // Expand f32 -> i64 conversion
   // This algorithm comes from compiler-rt's implementation of fixsfdi:
-  // https://github.com/llvm/llvm-project/blob/master/compiler-rt/lib/builtins/fixsfdi.c
+  // https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/builtins/fixsfdi.c
 
   unsigned SrcEltBits = SrcTy.getScalarSizeInBits();