build-llvm: Improve code for checking for preexisting native tools when cross compiling

Check for the prescence of the llvm-tblgen binary in addition to just
checking whether the llvm/build or llvm/build-asserts directories
exist.

In cases where having multiple build directories around, where some
are older than others, it's now possible to clarify which one to use
for tools by just removing the llvm-tblgen binary from the other ones.

Also check for the prescenece of each individual tool before setting
it; this fixes builds where the native build might not have all
components enable as as enabled in the cross build.

build-llvm.sh

@@ -145,16 +145,6 @@ else
 fi
 
 if [ -n "$HOST" ]; then
-    find_native_tools() {
-        if [ -d llvm-project/llvm/build/bin ]; then
-            echo $(pwd)/llvm-project/llvm/build/bin
-        elif [ -d llvm-project/llvm/build-asserts/bin ]; then
-            echo $(pwd)/llvm-project/llvm/build-asserts/bin
-        elif [ -n "$(which llvm-tblgen)" ]; then
-            echo $(dirname $(which llvm-tblgen))
-        fi
-    }
-
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_SYSTEM_NAME=Windows"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CROSSCOMPILING=TRUE"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_C_COMPILER=$HOST-gcc"
@@ -162,16 +152,40 @@ if [ -n "$HOST" ]; then
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_RC_COMPILER=$HOST-windres"
     CMAKEFLAGS="$CMAKEFLAGS -DCROSS_TOOLCHAIN_FLAGS_NATIVE="
 
-    native=$(find_native_tools)
-    if [ -n "$native" ]; then
+    native=""
+    for dir in llvm-project/llvm/build/bin llvm-project/llvm/build-asserts/bin; do
+        if [ -x "$dir/llvm-tblgen.exe" ]; then
+            native="$(pwd)/$dir"
+            suffix=".exe"
+            break
+        elif [ -x "$dir/llvm-tblgen" ]; then
+            native="$(pwd)/$dir"
+            suffix=""
+            break
+        fi
+    done
+    if [ -z "$native" ] && [ -n "$(which llvm-tblgen)" ]; then
+        native="$(dirname $(which llvm-tblgen))"
         suffix=""
-        if [ -f $native/llvm-tblgen.exe ]; then
+        if [ -x "$native/llvm-tblgen.exe" ]; then
             suffix=".exe"
         fi
-        CMAKEFLAGS="$CMAKEFLAGS -DLLVM_TABLEGEN=$native/llvm-tblgen$suffix"
-        CMAKEFLAGS="$CMAKEFLAGS -DCLANG_TABLEGEN=$native/clang-tblgen$suffix"
-        CMAKEFLAGS="$CMAKEFLAGS -DLLDB_TABLEGEN=$native/lldb-tblgen$suffix"
-        CMAKEFLAGS="$CMAKEFLAGS -DLLVM_CONFIG_PATH=$native/llvm-config$suffix"
+    fi
+
+
+    if [ -n "$native" ]; then
+        if [ -x "$native/llvm-tblgen$suffix" ]; then
+            CMAKEFLAGS="$CMAKEFLAGS -DLLVM_TABLEGEN=$native/llvm-tblgen$suffix"
+        fi
+        if [ -x "$native/clang-tblgen$suffix" ]; then
+            CMAKEFLAGS="$CMAKEFLAGS -DCLANG_TABLEGEN=$native/clang-tblgen$suffix"
+        fi
+        if [ -x "$native/lldb-tblgen$suffix" ]; then
+            CMAKEFLAGS="$CMAKEFLAGS -DLLDB_TABLEGEN=$native/lldb-tblgen$suffix"
+        fi
+        if [ -x "$native/llvm-config$suffix" ]; then
+            CMAKEFLAGS="$CMAKEFLAGS -DLLVM_CONFIG_PATH=$native/llvm-config$suffix"
+        fi
     fi
     CROSS_ROOT=$(cd $(dirname $(which $HOST-gcc))/../$HOST && pwd)
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH=$CROSS_ROOT"