[LLVM][Release] Prevent empty runtime name in release script

[DavidSpickett]

Summary

Unlike projects, runtimes doesn't have a default set of names.
This means you get a leading space at the start, which gets converted
to a ';' giving ";<runtime name>;<runtime name>".

CMake then errors because the "" before the first ';' is treated
as a runtime name and of course it's not a valid name.

Fix this by removing the leading spaces from runtimes before we
insert the ';'.

[DavidSpickett]

Clearly this worked at some point but now I get:

CMake Error at CMakeLists.txt:160 (message):
  Runtime is not a supported runtime.  Supported runtimes are:
  libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc

If you'd expect it to ignore the empty entry I can figure out what changed on that side instead.

[ldionne]

I think it makes more sense not to allow an empty entry (this patch) than implicitly ignore empty entries from within CMake. Thanks for fixing this.

llvm/utils/release/test-release.sh

case $Flavor in
         * )
             echo "# Invalid flavor '$Flavor'"
             echo ""
             return
             ;;
     esac
 
     project_list=${projects// /;}
+    # Leading spaces will result in ";<runtime name>". This causes a CMake
+    # error because the empty string before the first ';' is treated as an
+    # unknown runtime name.
+    runtimes=$(echo $runtimes | sed -e 's/^\s*//')
     runtime_list=${runtimes// /;}
     echo "# Using C compiler: $c_compiler"
     echo "# Using C++ compiler: $cxx_compiler"
 
     cd $ObjDir
     echo "# Configuring llvm $Release-$RC $Flavor"
 
     echo "#" env CC="$c_compiler" CXX="$cxx_compiler" \