Add a very simple stack printer for DFSan

[stephan.yichao.zhao]

Summary

Other sanitizers implemented their __sanitizer_print_stack_trace in much more complicated ways, not sure how to make DFSan's as complex as theirs...
This simple version works during my debugging.

[morehouse]

LGTM

compiler-rt/lib/dfsan/CMakeLists.txt

foreach(arch ${DFSAN_SUPPORTED_ARCH})
   append_list_if(COMPILER_RT_HAS_FPIE_FLAG -fPIE DFSAN_CFLAGS)
   add_compiler_rt_runtime(clang_rt.dfsan
     STATIC
     ARCHS ${arch}
     SOURCES ${DFSAN_RTL_SOURCES}
             $<TARGET_OBJECTS:RTInterception.${arch}>
             $<TARGET_OBJECTS:RTSanitizerCommon.${arch}>
             $<TARGET_OBJECTS:RTSanitizerCommonLibc.${arch}>
+            $<TARGET_OBJECTS:RTSanitizerCommonSymbolizer.${arch}>
     ADDITIONAL_HEADERS ${DFSAN_RTL_HEADERS}
     CFLAGS ${DFSAN_CFLAGS}
     PARENT_TARGET dfsan)
   add_sanitizer_rt_symbols(clang_rt.dfsan
     ARCHS ${arch}
     EXTRA dfsan.syms.extra)
   add_dependencies(dfsan
     clang_rt.dfsan-${arch}-symbols)

compiler-rt/lib/dfsan/dfsan.cpp

 
 #include "sanitizer_common/sanitizer_atomic.h"
 #include "sanitizer_common/sanitizer_common.h"
 #include "sanitizer_common/sanitizer_file.h"
 #include "sanitizer_common/sanitizer_flag_parser.h"
 #include "sanitizer_common/sanitizer_flags.h"
 #include "sanitizer_common/sanitizer_internal_defs.h"
 #include "sanitizer_common/sanitizer_libc.h"
+#include "sanitizer_common/sanitizer_stacktrace.h"
 
 using namespace __dfsan;
 
 typedef atomic_uint16_t atomic_dfsan_label;
 static const dfsan_label kInitializingLabel = -1;
 
 static const uptr kNumLabels = 1 << (sizeof(dfsan_label) * 8);
 
for (uptr l = 1; l <= last_label; ++l) {
     if (__dfsan_label_info[l].l1 == 0 && __dfsan_label_info[l].desc) {
       WriteToFile(fd, __dfsan_label_info[l].desc,
                   internal_strlen(__dfsan_label_info[l].desc));
     }
     WriteToFile(fd, "\n", 1);
   }
 }
 
+#define GET_FATAL_STACK_TRACE_PC_BP(pc, bp) \
+  BufferedStackTrace stack;                 \
+  stack.Unwind(pc, bp, nullptr, common_flags()->fast_unwind_on_fatal);
+
+void __sanitizer::BufferedStackTrace::UnwindImpl(uptr pc, uptr bp,
+                                                 void *context,
+                                                 bool request_fast,
+                                                 u32 max_depth) {
+  Unwind(max_depth, pc, bp, context, 0, 0, false);
+}
+
+extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_print_stack_trace() {
+  GET_FATAL_STACK_TRACE_PC_BP(StackTrace::GetCurrentPc(), GET_CURRENT_FRAME());
+  stack.Print();
+}
+
 void Flags::SetDefaults() {
 #define DFSAN_FLAG(Type, Name, DefaultValue, Description) Name = DefaultValue;
 #include "dfsan_flags.inc"
 #undef DFSAN_FLAG
 }
 
 static void RegisterDfsanFlags(FlagParser *parser, Flags *f) {
 #define DFSAN_FLAG(Type, Name, DefaultValue, Description) \