m4/acx_options.m4: remove double parenthesis

m4/acx_options.m4

@@ -553,7 +553,7 @@ AS_IF([test x$enable_cdi_lib = 'xno'],[AC_SUBST([ENABLE_CDI_LIB],[false])],[AC_S
 # scan for CDI as a subproject
 # AC_CONFIG_SUBDIRS([libcdi])
 CPPFLAGS="$CPPFLAGS -DCDI_SIZE_TYPE=size_t -DCDI_DATE_TYPE=int64_t"
-AX_SUBDIRS_CONFIGURE([libcdi], [], [[CPPFLAGS=-DCDI_SIZE_TYPE=size_t -DCDI_DATE_TYPE=int64_t]], [], [])
+AX_SUBDIRS_CONFIGURE([libcdi], [], [CPPFLAGS=-DCDI_SIZE_TYPE=size_t -DCDI_DATE_TYPE=int64_t], [], [])
 #  ----------------------------------------------------------------------
 #  Build a static CDO
 AC_MSG_CHECKING([for building an additional static CDO binary])