* It seems that some versions of the Intel compiler don't properly handle

the way we use weak symbols (you have to use the actual symbol in the
  .o file or the weak symbol isn't generated).  It worked for our test
  case, but not for libmpi.  Make our test case look more like what we
  do in libmpi by generating a .o file with a weak symbol and attempting
  to use it from another object file.

This commit was SVN r7360.

config/c_weak_symbols.m4

@@ -15,21 +15,49 @@ dnl
 dnl $HEADER$
 dnl
 
+# _OMPI_C_WEAK_SYMBOLS(action_if_found, [action_if_not_found])
+# ------------------------------------------------------------
+AC_DEFUN([_OMPI_C_WEAK_SYMBOLS],[
+    # need two files because icc will incorrectly not create the
+    # symbols if they are not used in the object file in which they
+    # are defined.  Blah!
+    cat > conftest_weak.c <<EOF
+extern int real(int i);
+extern int fake(int i);
+#pragma weak fake = real
+int real(int i) { return i; }
+EOF
+
+    cat > conftest.c <<EOF
+extern int fake(int i);
+extern int real(int i);
+int main(int argc, char *argv[]) { return fake(3); }
+EOF
+
+# Try the compile
+OMPI_LOG_COMMAND(
+    [$CC $CFLAGS  -c conftest_weak.c],
+    OMPI_LOG_COMMAND(
+        [$CC $CFLAGS  conftest.c conftest_weak.o -o conftest $LDFLAGS $LIBS],
+        [ompi_c_weak_symbols_happy=1],
+	[ompi_c_weak_symbols_happy=0]),
+    [ompi_c_weak_symbols_happy=0])
+
+    AS_IF([test "$ompi_c_weak_symbols_happy" = "1"], [$1], [$2])
+
+    unset ompi_c_weak_symbols_happy
+    /bin/rm -f conftest*
+])
+
+
 # OMPI_C_WEAK_SYMBOLS()
 # ---------------------
 # sets OMPI_C_WEAK_SYMBOLS=1 if C compiler has support for weak symbols
-define([OMPI_C_WEAK_SYMBOLS],[
-    AC_CACHE_CHECK([for weak symbols],
-                    [ompi_cv_c_weak_symbols],
-                    [AC_LINK_IFELSE([AC_LANG_SOURCE([[#pragma weak fake = real
-extern int fake(int i);
-int real(int i);
-int real(int i) { return i; }
-int main(int argc, char* argv[]) {
-  return fake(3);
-}]])],
-                                    [ompi_cv_c_weak_symbols="yes"],
-                                    [ompi_cv_c_weak_symbols="no"])])
+AC_DEFUN([OMPI_C_WEAK_SYMBOLS],[
+    AC_CACHE_CHECK([for weak symbol support],
+                   [ompi_cv_c_weak_symbols],
+                   [_OMPI_C_WEAK_SYMBOLS([ompi_cv_c_weak_symbols="yes"],
+                                         [ompi_cv_c_weak_symbols="no"])])
 
     AS_IF([test "$ompi_cv_c_weak_symbols" = "yes"],
           [OMPI_C_HAVE_WEAK_SYMBOLS=1], [OMPI_C_HAVE_WEAK_SYMBOLS=0])