[LSan] Export __lsan_init

Summary:
lsan_preinit.cc is meant to be linked into executable and calls
lsan_init from .preinit_array section. But if liblsan is a shared library,
then this doesn't work, because the symbol is not exported. This patch fixes
that. The counterparts like asan_init or __tsan_init already do have
SANITIZER_INTERFACE_ATTRIBUTE.

Committing on behalf of jakubjelinek.

Reviewers: alekseyshl, kcc

Subscribers: llvm-commits

Differential revision: https://reviews.llvm.org/D39889

llvm-svn: 318349

compiler-rt/lib/lsan/lsan.h

@@ -64,4 +64,4 @@ void GetStackTrace(__sanitizer::BufferedStackTrace *stack,
 extern bool lsan_inited;
 extern bool lsan_init_is_running;
 
-extern "C" void __lsan_init();
+extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __lsan_init();