nvim: Fix enum declaration of RemapValues

Instead of declaring an enum, this creates a global variable. As gcc10
uses -fno-common by default, global variables declared with the same
name more than once is not allowed anymore revealing this issue.

Each time this header is included, we define the enum name as a global
variable.

See also https://bugzilla.redhat.com/show_bug.cgi?id=1799680

src/nvim/getchar.h

@@ -10,12 +10,12 @@
 /// Values for "noremap" argument of ins_typebuf()
 ///
 /// Also used for map->m_noremap and menu->noremap[].
-enum {
+enum RemapValues {
   REMAP_YES = 0,  ///< Allow remapping.
   REMAP_NONE = -1,  ///< No remapping.
   REMAP_SCRIPT = -2,  ///< Remap script-local mappings only.
   REMAP_SKIP = -3,  ///< No remapping for first char.
-} RemapValues;
+};
 
 // Argument for flush_buffers().
 typedef enum {