Add fuzzing infrastructure

This commit adds the --enable-fuzzing (and --enable-asan, to make
fuzzing more useful) options and a sample fuzzer for the terminal
parser. At this time only libfuzzer is supported. Future changes to
add AFL to get more fuzzing capability should be possible with the
addition of the afl_driver.cc from Chromium.

configure.ac

@@ -68,6 +68,41 @@ AC_ARG_ENABLE([compile-warnings],
 AC_SUBST([WARNING_CXXFLAGS])
 AC_SUBST([PICKY_CXXFLAGS])
 
+# Check for fuzzing support before the flag wrapper, because if
+# requested and missing the functionality is entirely nonexistent.
+MISC_CXXFLAGS=""
+AC_ARG_ENABLE([fuzzing],
+  [AS_HELP_STRING([--enable-fuzzing],
+    [Enable compiler and linker options to enable fuzz testing @<:@no/yes/libfuzzer@:>@])],
+  [case "$enableval" in
+    no)
+      ;;
+    '' | yes | libfuzzer)
+      AX_CHECK_COMPILE_FLAG([-fsanitize=fuzzer],
+        [FUZZING_CFLAGS="$FUZZING_CFLAGS -fsanitize=fuzzer"], [
+        AC_MSG_ERROR([Fuzzing requested, but compiler support not present])], [-Werror])
+      ;;
+    *)
+     AC_MSG_ERROR(["Unknown argument '$enableval' to --enable-fuzzing])
+     ;;
+  esac],
+  [])
+AC_SUBST([FUZZING_CFLAGS])
+AC_SUBST([MISC_CXXFLAGS])
+
+AC_ARG_ENABLE([asan],
+  [AS_HELP_STRING([--enable-asan],
+    [Enable compiler and linker options to enable AddressSanitizer @<:@no@:>@])],
+  [asan="$enableval"],
+  [asan="no"])
+
+AS_IF([test x"$asan" != x"no"], [
+  AX_CHECK_COMPILE_FLAG([-fsanitize=address,leak],
+  [MISC_CXXFLAGS="$MISC_CXXFLAGS -fsanitize=address,leak"], [
+  AC_MSG_ERROR([ASAN requested, but compiler support not present])], [-Werror])
+])
+AC_SUBST([MISC_CXXFLAGS])
+
 # We want to check for compiler flag support, but there is no way to make
 # clang's "argument unused" warning fatal.  So we invoke the compiler through a
 # wrapper script that greps for this message.
@@ -119,7 +154,6 @@ AC_SUBST([HARDEN_CFLAGS])
 AC_SUBST([HARDEN_LDFLAGS])
 
 # Also check for a few non-hardening-related flags.
-MISC_CXXFLAGS=""
 AX_CHECK_COMPILE_FLAG([-fno-default-inline],
   [MISC_CXXFLAGS="$MISC_CXXFLAGS -fno-default-inline"], [], [-Werror])
 AX_CHECK_COMPILE_FLAG([-pipe],
@@ -526,6 +560,7 @@ AC_CONFIG_FILES([
   src/Makefile
   src/crypto/Makefile
   src/frontend/Makefile
+  src/fuzz/Makefile
   src/include/Makefile
   src/network/Makefile
   src/protobufs/Makefile