New --enable-expensive-hardening option

It turns on -fsanitize=address and -fsanitize=ubsan if they work.

Most relays won't want this. Some clients may.  Ticket 11477.

changes/bug11477

@@ -0,0 +1,4 @@
+  o Minor features:
+    - New --enable-expensive-hardening option to turn on security hardening
+      options that consume nontrivial amounts of CPU and memory. Right now,
+      this includes AddressSanitizer and UbSan. Closes ticket 11477.

configure.ac

@@ -129,13 +129,13 @@ AC_ARG_ENABLE(gcc-warnings,
 AC_ARG_ENABLE(gcc-warnings-advisory,
      AS_HELP_STRING(--enable-gcc-warnings-advisory, [enable verbose warnings, excluding -Werror]))
 
-dnl Adam shostack suggests the following for Windows:
-dnl -D_FORTIFY_SOURCE=2 -fstack-protector-all
 dnl Others suggest '/gs /safeseh /nxcompat /dynamicbase' for non-gcc on Windows
-dnl This requires that we use gcc and that we add -O2 to the CFLAGS.
 AC_ARG_ENABLE(gcc-hardening,
     AS_HELP_STRING(--disable-gcc-hardening, disable compiler security checks))
 
+AC_ARG_ENABLE(expensive-hardening,
+    AS_HELP_STRING(--enable-expensive-hardening, enable more expensive compiler hardening; makes Tor slower))
+
 dnl Linker hardening options
 dnl Currently these options are ELF specific - you can't use this with MacOSX
 AC_ARG_ENABLE(linker-hardening,
@@ -628,6 +628,12 @@ if test x$enable_gcc_hardening != xno; then
     fi
 fi
 
+if test x$enable_expensive_hardening = xyes ; then
+   TOR_CHECK_CFLAGS([-fsanitize=address])
+   TOR_CHECK_CFLAGS([-fsanitize=undefined])
+   TOR_CHECK_CFLAGS([-fno-omit-frame-pointer])
+fi
+
 if test x$enable_linker_hardening != xno; then
     TOR_CHECK_LDFLAGS(-z relro -z now, "$all_ldflags_for_check", "$all_libs_for_check")
 fi
@@ -640,10 +646,11 @@ dnl Now see if we have a -fomit-frame-pointer compiler option.
 
 saved_CFLAGS="$CFLAGS"
 TOR_CHECK_CFLAGS(-fomit-frame-pointer)
+F_OMIT_FRAME_POINTER=''
 if test "$saved_CFLAGS" != "$CFLAGS"; then
-  F_OMIT_FRAME_POINTER='-fomit-frame-pointer'
-else
-  F_OMIT_FRAME_POINTER=''
+  if test x$enable_expensive_hardening != xyes ; then
+    F_OMIT_FRAME_POINTER='-fomit-frame-pointer'
+  fi
 fi
 CFLAGS="$saved_CFLAGS"
 AC_SUBST(F_OMIT_FRAME_POINTER)