fuzz: Hide conflicts with cstdlib and use clang++ for linking.

This creates a build target called libec.a by setting the visibility
of functions that conflict with cstdlib to hidden. It then links
those symbols locally into one large object file that makes up libec.a

Fuzzing targets are linked against libec.a so that they can invoke ec
functionality while depending on outside libraries that need cstdlib.
When linking a particular object against cstdlib, to avoid conflicting
function declarations put the following before any includes from the
ec codebase:
   #define __stdlib_compat(...)

The fuzzing targets are now linked using clang++, so that c++ libraries
and objects can be used as part of the fuzzers.

BRANCH=none
BUG=chromium:876582
TEST=make -j buildfuzztests &&
  ./build/host/host_command_fuzz/host_command_fuzz.exe

Change-Id: Ifdfdc6a51c6ef23b4e192b013ca993bf48a4411b
Signed-off-by: Allen Webb <allenwebb@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1180401
Reviewed-by: Randall Spangler <rspangler@chromium.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/trng.h b/include/trng.h
index ec56829e54..e50b12a2a6 100644
--- a/include/trng.h
+++ b/include/trng.h
@@ -5,6 +5,7 @@
 #ifndef __EC_INCLUDE_TRNG_H
 #define __EC_INCLUDE_TRNG_H
 
+#include <common.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -30,7 +31,9 @@ void exit_trng(void);
  *
  * Not supported on all platforms.
  **/
-uint32_t rand(void);
+#ifndef HIDE_EC_STDLIB
+__stdlib_compat uint32_t rand(void);
+#endif
 
 /**
  * Output len random bytes into buffer.