gnu: Add NetCDF.

* gnu/packages/maths.scm (netcdf, netcdf-parallel-openmpi): New variables.

gnu/packages/patches/netcdf-config-date.patch

@@ -0,0 +1,47 @@
+Honor SOURCE_DATE_EPOCH when exporting configuration date.
+Autoconf-level patch submitted upstream on Fri Apr 15 23:07:42 UTC 2016
+
+--- a/configure
++++ b/configure
+@@ -2866,7 +2866,17 @@
+ 
+ 
+ # Configuration Date
+- CONFIG_DATE="`date`"
++ CONFIG_DATE="`date -u`"
++if test -n "$SOURCE_DATE_EPOCH"; then
++  CONFIG_DATE=`date -u -d "@$SOURCE_DATE_EPOCH" 2>/dev/null \
++               || date -u -r "$SOURCE_DATE_EPOCH" 2>/dev/null`
++  if test -z "$CONFIG_DATE"; then
++    as_fn_error $? "malformed SOURCE_DATE_EPOCH" "$LINENO" 5
++  fi
++fi
++cat >>confdefs.h <<_ACEOF
++#define CONFIG_DATE "$CONFIG_DATE"
++_ACEOF
+ 
+ # Find out about the host we're building on.
+ ac_aux_dir=
+--- a/libdispatch/derror.c
++++ b/libdispatch/derror.c
+@@ -13,7 +13,7 @@
+ #endif
+ 
+ /* Tell the user the version of netCDF. */
+-static const char nc_libvers[] = PACKAGE_VERSION " of "__DATE__" "__TIME__" $";
++static const char nc_libvers[] = PACKAGE_VERSION " of "CONFIG_DATE" $";
+ 
+ /**
+ \defgroup lib_version Library Version
+--- a/config.h.in
++++ b/config.h.in
+@@ -393,6 +393,9 @@
+ /* Define to the version of this package. */
+ #undef PACKAGE_VERSION
+ 
++/* Define to the configuration date */
++#undef CONFIG_DATE
++
+ /* The size of `double', as computed by sizeof. */
+ #undef SIZEOF_DOUBLE
+