Add --with-sanitizers option to configure

This enables the use of different compiler sanitizers, coresponding to
the -fsanitize option in GCC and Clang.

configure.ac

@@ -219,6 +219,12 @@ AC_ARG_ENABLE([debug],
     [enable_debug=$enableval],
     [enable_debug=no])
 
+# Enable different -fsanitize options
+AC_ARG_WITH([sanitizers],
+    [AS_HELP_STRING([--with-sanitizers],
+                    [comma separated list of extra sanitizers to build with (default is none enabled)])],
+    [use_sanitizers=$withval])
+
 # Enable gprof profiling
 AC_ARG_ENABLE([gprof],
     [AS_HELP_STRING([--enable-gprof],
@@ -247,6 +253,26 @@ if test "x$enable_debug" = xyes; then
     fi
 fi
 
+if test x$use_sanitizers != x; then
+  # First check if the compiler accepts flags. If an incompatible pair like
+  # -fsanitize=address,thread is used here, this check will fail. This will also
+  # fail if a bad argument is passed, e.g. -fsanitize=undfeined
+  AX_CHECK_COMPILE_FLAG(
+    [[-fsanitize=$use_sanitizers]],
+    [[SANITIZER_CXXFLAGS=-fsanitize=$use_sanitizers]],
+    [AC_MSG_ERROR([compiler did not accept requested flags])])
+
+  # Some compilers (e.g. GCC) require additional libraries like libasan,
+  # libtsan, libubsan, etc. Make sure linking still works with the sanitize
+  # flag. This is a separate check so we can give a better error message when
+  # the sanitize flags are supported by the compiler but the actual sanitizer
+  # libs are missing.
+  AX_CHECK_LINK_FLAG(
+    [[-fsanitize=$use_sanitizers]],
+    [[SANITIZER_LDFLAGS=-fsanitize=$use_sanitizers]],
+    [AC_MSG_ERROR([linker did not accept requested flags, you are missing required libraries])])
+fi
+
 ERROR_CXXFLAGS=
 if test "x$enable_werror" = "xyes"; then
   if test "x$CXXFLAG_WERROR" = "x"; then
@@ -1258,6 +1284,8 @@ AC_SUBST(HARDENED_CPPFLAGS)
 AC_SUBST(HARDENED_LDFLAGS)
 AC_SUBST(PIC_FLAGS)
 AC_SUBST(PIE_FLAGS)
+AC_SUBST(SANITIZER_CXXFLAGS)
+AC_SUBST(SANITIZER_LDFLAGS)
 AC_SUBST(SSE42_CXXFLAGS)
 AC_SUBST(LIBTOOL_APP_LDFLAGS)
 AC_SUBST(USE_UPNP)