build-llvm: Stop setting -DCROSS_TOOLCHAIN_FLAGS_NATIVE=

Since 93010544a813dfbfa64dd7cee68785f572f974d1 in llvm-project
(Jun 22nd), this no longer is needed for being able to build
native tools with a nested cmake in a cross build. (If building in
the same tree as a previous native build, build-llvm tries to pick
up the tblgen tools from there, so in such cases, this doesn't
make any difference and the nested native cmake invocation never
was executed.)

build-llvm.sh

@@ -152,7 +152,6 @@ if [ -n "$HOST" ]; then
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_C_COMPILER=$HOST-gcc"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CXX_COMPILER=$HOST-g++"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_RC_COMPILER=$HOST-windres"
-    CMAKEFLAGS="$CMAKEFLAGS -DCROSS_TOOLCHAIN_FLAGS_NATIVE="
 
     native=""
     for dir in llvm-project/llvm/build/bin llvm-project/llvm/build-asserts/bin; do