Update git submodules

* Update external/protobuf from branch 'master'
  to 50b1364f5d2f50c91efd797259eabb956373a36b
  - Merge "Moved contents of clang_cflags into cflags"
  - Moved contents of clang_cflags into cflags
    
    Test: Treehugger
    Bug: 226636335
    Change-Id: I00274613925697a8b59eb2b2fd671c1985d3b89d
    
1 file changed