scons: force libasan to static linking

The asan(enable with --with-asan) sanitizer interpret calls to dlopen().
That replaces the RUNPATH of an executable with RUNPATH of libasan.so
after libasan.so is loaded by loader. Then it may cause some shared
libraries missing, i.e. the error messages is like
"cannot open shared object file: No such file or directory" since the
RUNPATH is no longer correct. Force the libasan to static linking
can avoid this issue since libasan.a does not have a RUNPATH, thus
the replacement will never happen.

Change-Id: I8e5ff4d1fbe4644a258054be6e9f6d4db9062e56
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67298
Reviewed-by: Earl Ou <shunhsingou@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>

SConstruct

@@ -526,7 +526,9 @@ for variant_path in variant_paths:
         if env['GCC'] or env['CLANG']:
             env.Append(CCFLAGS=['-fsanitize=%s' % sanitizers,
                                  '-fno-omit-frame-pointer'],
-                        LINKFLAGS='-fsanitize=%s' % sanitizers)
+                        LINKFLAGS=['-fsanitize=%s' % sanitizers,
+                                   '-static-libasan'])
+
             if main["BIN_TARGET_ARCH"] == "x86_64":
                 # Sanitizers can enlarge binary size drammatically, north of
                 # 2GB.  This can prevent successful linkage due to symbol