[asan][cmake][test] Fix finding dynamic asan runtime lib (#100083)

In a `runtimes` build on Solaris/amd64, there are two failues:
```
  AddressSanitizer-Unit :: ./Asan-i386-calls-Dynamic-Test/failed_to_discover_tests_from_gtest
  AddressSanitizer-Unit :: ./Asan-i386-inline-Dynamic-Test/failed_to_discover_tests_from_gtest
```
This happens when `lit` enumerates the tests with `--gtest_list_tests
--gtest_filter=-*DISABLED_*`. The error is twofold:

- The `LD_LIBRARY_PATH*` variables point at the 64-bit directory
(`lib/clang/19/lib/x86_64-pc-solaris2.11`) for a 32-bit test:
  ```
ld.so.1: Asan-i386-calls-Dynamic-Test: fatal:
/var/llvm/local-amd64-release-stage2-A-flang-clang18-runtimes/tools/clang/stage2-bins/./lib/../lib/clang/19/lib/x86_64-pc-solaris2.11/libclang_rt.asan.so:
wrong ELF class: ELFCLASS64
  ```
- While the tests are linked with `-Wl,-rpath`, that path always is the
64-bit directory again.

Accordingly, the fix consists of two parts:
- The code in `compiler-rt/test/asan/Unit/lit.site.cfg.py.in` to adjust
the `LD_LIBRARY_PATH*` variables is guarded by a `config.target_arch !=
config.host_arch` condition. This is wrong in two ways:
- The adjustment is always needed independent of the host arch. This is
what `compiler-rt/test/lit.common.cfg.py` already does.
- Besides, `config.host_arch` is ultimately set from
`CMAKE_HOST_SYSTEM_PROCESSOR`. On Linux/x86_64, this is `x86_64` (`uname
-m`) while on Solaris/amd64 it's `i386` (`uname -p`), explaining why the
transformation is skipped on Solaris, but not on Linux.
- Besides, `RPATH` needs to be set to the correct subdirectory, so
instead of using the default arch in `compiler-rt/CMakeLists.txt`, this
patch moves the code to a function which takes the test's arch into
account.

Tested on `amd64-pc-solaris2.11` and `x86_64-pc-linux-gnu`.

(cherry picked from commit c34d673b02ead039acd107f096c1f32c16b61e07)

compiler-rt/CMakeLists.txt

@@ -604,10 +604,6 @@ if (COMPILER_RT_TEST_STANDALONE_BUILD_LIBS)
   if ("${COMPILER_RT_TEST_COMPILER_ID}" MATCHES "Clang")
     list(APPEND COMPILER_RT_UNITTEST_LINK_FLAGS "-resource-dir=${COMPILER_RT_OUTPUT_DIR}")
   endif()
-  get_compiler_rt_output_dir(${COMPILER_RT_DEFAULT_TARGET_ARCH} rtlib_dir)
-  if (NOT WIN32)
-    list(APPEND COMPILER_RT_UNITTEST_LINK_FLAGS "-Wl,-rpath,${rtlib_dir}")
-  endif()
 endif()
 
 if(COMPILER_RT_USE_LLVM_UNWINDER)

compiler-rt/cmake/config-ix.cmake

@@ -267,6 +267,19 @@ function(get_target_link_flags_for_arch arch out_var)
   endif()
 endfunction()
 
+# Returns a list of architecture specific dynamic ldflags in @out_var list.
+function(get_dynamic_link_flags_for_arch arch out_var)
+  list(FIND COMPILER_RT_SUPPORTED_ARCH ${arch} ARCH_INDEX)
+  if(ARCH_INDEX EQUAL -1)
+    message(FATAL_ERROR "Unsupported architecture: ${arch}")
+  else()
+    get_compiler_rt_output_dir(${arch} rtlib_dir)
+    if (NOT WIN32)
+      set(${out_var} "-Wl,-rpath,${rtlib_dir}" PARENT_SCOPE)
+    endif()
+  endif()
+endfunction()
+
 # Returns a compiler and CFLAGS that should be used to run tests for the
 # specific architecture.  When cross-compiling, this is controled via
 # COMPILER_RT_TEST_COMPILER and COMPILER_RT_TEST_COMPILER_CFLAGS.

compiler-rt/lib/asan/tests/CMakeLists.txt

@@ -206,13 +206,15 @@ function(add_asan_tests arch test_runtime)
           -Wl,-nodefaultlib:libcmt,-defaultlib:msvcrt,-defaultlib:oldnames
         )
     else()
+      set(DYNAMIC_LINK_FLAGS)
+      get_dynamic_link_flags_for_arch(${arch} DYNAMIC_LINK_FLAGS)
 
       # Otherwise, reuse ASAN_INST_TEST_OBJECTS.
       add_compiler_rt_test(AsanDynamicUnitTests "${dynamic_test_name}" "${arch}"
         SUBDIR "${CONFIG_NAME_DYNAMIC}"
         OBJECTS ${ASAN_INST_TEST_OBJECTS}
         DEPS asan ${ASAN_INST_TEST_OBJECTS}
-        LINK_FLAGS ${ASAN_DYNAMIC_UNITTEST_INSTRUMENTED_LINK_FLAGS} ${TARGET_LINK_FLAGS}
+        LINK_FLAGS ${ASAN_DYNAMIC_UNITTEST_INSTRUMENTED_LINK_FLAGS} ${TARGET_LINK_FLAGS} ${DYNAMIC_LINK_FLAGS}
         )
     endif()
   endif()

compiler-rt/test/asan/Unit/lit.site.cfg.py.in

@@ -53,7 +53,7 @@ config.test_source_root = config.test_exec_root
 # host triple as the trailing path component. The value is incorrect for i386
 # tests on x86_64 hosts and vice versa. Adjust config.compiler_rt_libdir
 # accordingly.
-if config.enable_per_target_runtime_dir and config.target_arch != config.host_arch:
+if config.enable_per_target_runtime_dir:
     if config.target_arch == 'i386':
         config.compiler_rt_libdir = re.sub(r'/x86_64(?=-[^/]+$)', '/i386', config.compiler_rt_libdir)
     elif config.target_arch == 'x86_64':