[compiler-rt] Propagate sysroot from CMake to msan tests

Some msan tests requires rpc/xdr.h, which is no longer available
in some newer glibc. In build systems with hermetic sysroot set through
CMake, this issue can be solved by setting the sysroot to CMAKE_SYSROOT
for these tests. This patch implements it.

Author: zeroomega

compiler-rt/test/msan/lit.cfg.py

@@ -17,6 +17,10 @@
         "-fno-optimize-sibling-calls",
     ]
     + [config.target_cflags]
+    + [
+        "--sysroot",
+        config.cmake_sysroot
+    ] if config.cmake_sysroot and config.host_os == "Linux" else []
     + config.debug_info_flags
 )
 # Some Msan tests leverage backtrace() which requires libexecinfo on FreeBSD.

compiler-rt/test/msan/lit.site.cfg.py.in

@@ -6,6 +6,7 @@ config.target_cflags = "@MSAN_TEST_TARGET_CFLAGS@"
 config.target_arch = "@MSAN_TEST_TARGET_ARCH@"
 config.use_lld = @MSAN_TEST_USE_LLD@
 config.use_thinlto = @MSAN_TEST_USE_THINLTO@
+config.cmake_sysroot = "@CMAKE_SYSROOT@"
 
 # Load common config for all compiler-rt lit tests.
 lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/test/lit.common.configured")