Resolve CFLAGS_JIT at configure-time

Author: zanieb

configure

@@ -2752,7 +2752,6 @@ AS_VAR_IF([ac_cv_gcc_compat], [yes], [
 ])
 
 # Check for --enable-experimental-jit:
-AC_SUBST([CFLAGS_JIT])
 AC_MSG_CHECKING([for --enable-experimental-jit])
 AC_ARG_ENABLE([experimental-jit],
               [AS_HELP_STRING([--enable-experimental-jit@<:@=no|yes|yes-off|interpreter@:>@],
@@ -2777,7 +2776,7 @@ AS_VAR_IF([jit_flags],
           [],
           [AS_VAR_APPEND([CFLAGS_NODIST], [" $jit_flags"])
            AS_VAR_SET([REGEN_JIT_COMMAND],
-                      ["\$(PYTHON_FOR_REGEN) \$(srcdir)/Tools/jit/build.py ${ARCH_TRIPLES:-$host} --output-dir . --pyconfig-dir . --cflags=\"\$(CFLAGS_JIT)\""])
+                      ["\$(PYTHON_FOR_REGEN) \$(srcdir)/Tools/jit/build.py ${ARCH_TRIPLES:-$host} --output-dir . --pyconfig-dir . --cflags=\"$CFLAGS_JIT\""])
            AS_VAR_SET([JIT_STENCILS_H], ["jit_stencils.h"])
            AS_VAR_IF([Py_DEBUG],
                      [true],