Octave: disable optimization of tests for faster compiles/less memory usage

- Filter out all but -g... and -W... flags from OCTAVE_CXXFLAGS
- Use AX_CHECK_COMPILE_FLAG() to check if -O0 is supported, if so
  add to end of OCTAVE_CXXFLAGS to ensure optimization is disabled
- Also run mkoctfile under "env -" to protect it from environment
- Also use more standard-compliant sed expressions

configure.ac

@@ -937,25 +937,43 @@ fi
 if test -n "$OCTAVE"; then
    AC_MSG_CHECKING([for Octave preprocessor flags])
    OCTAVE_CPPFLAGS=
-   for n in CPPFLAGS INCFLAGS; do
-     OCTAVE_CPPFLAGS="${OCTAVE_CPPFLAGS} "`unset CPPFLAGS; ${mkoctfile} -p $n`
+   for var in CPPFLAGS INCFLAGS ALL_CXXFLAGS; do
+      for flag in `env - ${mkoctfile} -p ${var}`; do
+         case ${flag} in
+            -D*|-I*) OCTAVE_CPPFLAGS="${OCTAVE_CPPFLAGS} ${flag}";;
+            *) ;;
+         esac
+      done
    done
    AC_MSG_RESULT([$OCTAVE_CPPFLAGS])
    AC_MSG_CHECKING([for Octave compiler flags])
    OCTAVE_CXXFLAGS=
-   for n in ALL_CXXFLAGS; do
-     OCTAVE_CXXFLAGS="${OCTAVE_CXXFLAGS} "`unset CXXFLAGS; ${mkoctfile} -p $n`
+   for var in ALL_CXXFLAGS; do
+      for flag in `env - ${mkoctfile} -p ${var}`; do
+         case ${flag} in
+            -g*|-W*) OCTAVE_CXXFLAGS="${OCTAVE_CXXFLAGS} ${flag}";;
+            *) ;;
+         esac
+      done
    done
+   save_CXXFLAGS="${CXXFLAGS}"
+   CXXFLAGS="-Werror -O0"
+   AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT],[])
+   ],[
+      OCTAVE_CXXFLAGS="${OCTAVE_CXXFLAGS} -O0"
+   ])
+   CXXFLAGS="${save_CXXFLAGS}"
    AC_MSG_RESULT([$OCTAVE_CXXFLAGS])
    AC_MSG_CHECKING([for Octave linker flags])
    OCTAVE_LDFLAGS=
-   for n in RDYNAMIC_FLAG LFLAGS RLD_FLAG OCTAVE_LIBS LIBS; do
-     OCTAVE_LDFLAGS="${OCTAVE_LDFLAGS} "`${mkoctfile} -p $n`
+   for var in RDYNAMIC_FLAG LFLAGS RLD_FLAG OCTAVE_LIBS LIBS; do
+     OCTAVE_LDFLAGS="${OCTAVE_LDFLAGS} "`env - ${mkoctfile} -p ${var}`
    done
    AC_MSG_RESULT([$OCTAVE_LDFLAGS])
    for octave_opt in --silent --norc --no-history --no-window-system; do
       AC_MSG_CHECKING([if Octave option '${octave_opt}' is supported])
-      octave_out=`${OCTAVE} ${octave_opt} /dev/null 2>&1 | sed -n '1{/unrecognized/p}'`
+      octave_out=`${OCTAVE} ${octave_opt} /dev/null 2>&1 | sed -n '1p' | sed -n '/unrecognized/p'`
       AS_IF([test "x${octave_out}" = x],[
          AC_MSG_RESULT([yes])
          OCTAVE="${OCTAVE} ${octave_opt}"