Try to manually test for whether the compiler hardening flags work

Also, make the check for whether they're on by default work; there's
no need to mess around with this "$enableval" silliness.

acinclude.m4

@@ -41,6 +41,40 @@ AC_DEFUN([TOR_DEFINE_CODEPATH],
   AC_SUBST(TOR_LDFLAGS_$2)
 ])
 
+dnl 1:flags
+AC_DEFUN([TOR_CHECK_CFLAGS], [
+  AS_VAR_PUSHDEF([VAR],[tor_cv_cflags_$1])
+  AC_CACHE_CHECK([whether the compiler accepts $1], VAR, [
+    tor_saved_CFLAGS="$CFLAGS"
+    CFLAGS="$CFLAGS $1"
+    AC_TRY_COMPILE([], [return 0;],
+                   [AS_VAR_SET(VAR,yes)],
+                   [AS_VAR_SET(VAR,no)])
+    CFLAGS="$tor_saved_CFLAGS"
+  ])
+  if test x$VAR = xyes; then
+    CFLAGS="$CFLAGS $1"
+  fi
+  AS_VAR_POPDEF([VAR])
+])
+
+dnl 1:flags
+AC_DEFUN([TOR_CHECK_LDFLAGS], [
+  AS_VAR_PUSHDEF([VAR],[tor_cv_ldflags_$1])
+  AC_CACHE_CHECK([whether the linker accepts $1], VAR, [
+    tor_saved_LDFLAGS="$LDFLAGS"
+    LDFLAGS="$LDFLAGS $1"
+    AC_TRY_LINK([], [return 0;],
+                   [AS_VAR_SET(VAR,yes)],
+                   [AS_VAR_SET(VAR,no)])
+    LDFLAGS="$tor_saved_LDFLAGS"
+  ])
+  if test x$VAR = xyes; then
+    LDFLAGS="$LDFLAGS $1"
+  fi
+  AS_VAR_POPDEF([VAR])
+])
+
 dnl 1:libname
 AC_DEFUN([TOR_WARN_MISSING_LIB], [
 h=""

configure.in

@@ -122,25 +122,12 @@ 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),
-    [],
-    [enableval=yes;])
-[if test x$enableval = xyes; then
-    CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2 -fstack-protector-all"
-    CFLAGS="$CFLAGS -fwrapv -fPIE -Wstack-protector"
-    CFLAGS="$CFLAGS --param ssp-buffer-size=1"
-    LDFLAGS="$LDFLAGS -pie"
-fi]
+    AS_HELP_STRING(--disable-gcc-hardening, disable compiler security checks))
 
 dnl Linker hardening options
 dnl Currently these options are ELF specific - you can't use this with MacOSX
 AC_ARG_ENABLE(linker-hardening,
-    AS_HELP_STRING(--disable-linker-hardening, disable linker security fixups),
-    [],
-    [enableval=yes;])
-AC_CHECK_HEADER([elf.h], [if test x$enableval = xyes; then
-    LDFLAGS="$LDFLAGS -z relro -z now"
-fi])
+    AS_HELP_STRING(--disable-linker-hardening, disable linker security fixups))
 
 AC_ARG_ENABLE(local-appdata,
    AS_HELP_STRING(--enable-local-appdata, default to host local application data paths on Windows))
@@ -184,6 +171,20 @@ AM_CONDITIONAL(NAT_PMP, test x$natpmp = xtrue)
 AM_CONDITIONAL(MINIUPNPC, test x$upnp = xtrue)
 AM_PROG_CC_C_O
 
+if test x$enable_gcc_hardening != xno; then
+    CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2"
+    TOR_CHECK_CFLAGS(-fstack-protector-all)
+    TOR_CHECK_CFLAGS(-Wstack-protector)
+    TOR_CHECK_CFLAGS(-fwrapv)
+    TOR_CHECK_CFLAGS(-fPIE)
+    TOR_CHECK_CFLAGS(--param ssp-buffer-size=1)
+    TOR_CHECK_LDFLAGS(-pie)
+fi
+
+if test x$enable_linker_hardening != xno; then
+    TOR_CHECK_LDFLAGS(-z relro -z now)
+fi
+
 ifdef([AC_C_FLEXIBLE_ARRAY_MEMBER], [
 AC_C_FLEXIBLE_ARRAY_MEMBER
 ], [