Fix flang-aarch64-libcxx builder (#432)

After flang-rt, flang-aarch64-libcxx builder started to fail.
Before it, llvm libraries, flang and its runtime were built with the
host compiler, but now flang runtime is built with the stage 1 clang.
The problem is that the C++ library of these compilers may be
incompatible. The linked issue has more details.

To avoid this issue, use the out of tree flang builder to build llvm,
flang and flang-rt with the host compiler, using libcxx.

Fixes llvm/llvm-project#135381

Author: luporl

buildbot/osuosl/master/config/builders.py

@@ -2527,21 +2527,27 @@
     'tags'  : ['flang'],
     'workernames' : ["linaro-flang-aarch64-libcxx"],
     'builddir': "flang-aarch64-libcxx",
-    'factory' : UnifiedTreeBuilder.getCmakeWithNinjaBuildFactory(
-                    clean=True,
-                    checks=['check-flang','check-flang-rt'],
-                    depends_on_projects=['llvm','mlir','clang','flang','flang-rt'],
-                    extra_configure_args=[
+    'factory' : FlangBuilder.getFlangOutOfTreeBuildFactory(
+                    checks=['check-flang'],
+                    llvm_extra_configure_args=[
                         "-DLLVM_TARGETS_TO_BUILD=AArch64",
-                        "-DLLVM_INSTALL_UTILS=ON",
                         "-DCMAKE_CXX_STANDARD=17",
                         "-DLLVM_ENABLE_WERROR=OFF",
+                        "-DLLVM_ENABLE_ASSERTIONS=ON",
+                        "-DLLVM_ENABLE_LIBCXX=On",
+                        "-DCMAKE_BUILD_TYPE=Release",
+                    ],
+                    flang_extra_configure_args=[
                         "-DFLANG_ENABLE_WERROR=ON",
-                        "-DBUILD_SHARED_LIBS=ON",
                         "-DLLVM_ENABLE_ASSERTIONS=ON",
                         "-DLLVM_ENABLE_LIBCXX=On",
                         "-DCMAKE_BUILD_TYPE=Release",
-                        ])},
+                    ],
+                    flang_rt_extra_configure_args=[
+                        "-DLLVM_ENABLE_ASSERTIONS=ON",
+                        "-DLLVM_ENABLE_LIBCXX=On",
+                        "-DCMAKE_BUILD_TYPE=Release",
+                    ])},
 
     {'name' : "flang-aarch64-release",
     'tags'  : ["flang"],