build-llvm: Use the built-in recursive cmake for building llvm-tblgen if necessary

This requires setting a flag to use the system default compiler
for this, instead of the cross compiler.

build-llvm.sh

@@ -96,27 +96,20 @@ if [ -n "$HOST" ]; then
             echo $(dirname $(which llvm-tblgen))
         fi
     }
-    native=$(find_native_tools)
-    if [ -z "$native" ]; then
-        # As we don't do any install here, the target prefix shouldn't actually
-        # be created.
-        HOST="" BUILDTARGETS="llvm-tblgen clang-tblgen llvm-config" $0 $PREFIX/llvmtools
-        native=$(find_native_tools)
-        if [ -z "$native" ]; then
-            echo Unable to find the newly built llvm-tblgen
-            exit 1
-        fi
-    fi
 
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_SYSTEM_NAME=Windows"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CROSSCOMPILING=TRUE"
     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="
 
-    CMAKEFLAGS="$CMAKEFLAGS -DLLVM_TABLEGEN=$native/llvm-tblgen"
-    CMAKEFLAGS="$CMAKEFLAGS -DCLANG_TABLEGEN=$native/clang-tblgen"
-    CMAKEFLAGS="$CMAKEFLAGS -DLLVM_CONFIG_PATH=$native/llvm-config"
+    native=$(find_native_tools)
+    if [ -n "$native" ]; then
+        CMAKEFLAGS="$CMAKEFLAGS -DLLVM_TABLEGEN=$native/llvm-tblgen"
+        CMAKEFLAGS="$CMAKEFLAGS -DCLANG_TABLEGEN=$native/clang-tblgen"
+        CMAKEFLAGS="$CMAKEFLAGS -DLLVM_CONFIG_PATH=$native/llvm-config"
+    fi
     CROSS_ROOT=$(cd $(dirname $(which $HOST-gcc))/../$HOST && pwd)
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH=$CROSS_ROOT"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER"