Add hook for Unicode private use override

I am starting to write a Unicode::Private_Use module which will allow
one to specify the Unicode properties of private use code points, thus
making them actually useful.  This commit adds a hook to regcomp.c to
accommodate this module.  The changes are pretty minimal.  This way we
don't have to wait another release cycle to get it out there.

I don't want to document this interface, until it's proven.

Author: khwilliamson

MANIFEST

@@ -4771,6 +4771,7 @@ lib/unicore/ScriptExtensions.txt		Unicode character database
 lib/unicore/Scripts.txt				Unicode character database
 lib/unicore/SpecialCasing.txt			Unicode character database
 lib/unicore/StandardizedVariants.txt		Unicode character database
+lib/unicore/uni_keywords.pl			Indices into array in charclass_invlists.h
 lib/unicore/UnicodeData.txt			Unicode character database
 lib/unicore/version				The version of the Unicode
 lib/unicore/VerticalOrientation.txt		Unicode character database

charclass_invlists.h

@@ -390181,5 +390181,5 @@ static const U8 WB_table[23][23] = {
  * 93cc868487ef3345596041bcb90c302b1b056733bb95233101bc10dc2dbe36b4 lib/unicore/version
  * 2680b9254eb236c5c090f11b149605043e8c8433661b96efc4a42fb4709342a5 regen/charset_translations.pl
  * 03e51b0f07beebd5da62ab943899aa4934eee1f792fa27c1fb638c33bf4ac6ea regen/mk_PL_charclass.pl
- * 2fb19108265d37fc38920cd3f775c5c9fc25ae8b95be3bf197f47da1dc4989f4 regen/mk_invlists.pl
+ * d62728e4cfcba3e6550ff12ad924f4811ca2077ebec705b9fecabed716764414 regen/mk_invlists.pl
  * ex: set ro: */

embedvar.h

@@ -371,6 +371,8 @@
 #define PL_GNonFinalFold	(my_vars->GNonFinalFold)
 #define PL_Posix_ptrs		(my_vars->GPosix_ptrs)
 #define PL_GPosix_ptrs		(my_vars->GPosix_ptrs)
+#define PL_Private_Use		(my_vars->GPrivate_Use)
+#define PL_GPrivate_Use		(my_vars->GPrivate_Use)
 #define PL_SB_invlist		(my_vars->GSB_invlist)
 #define PL_GSB_invlist		(my_vars->GSB_invlist)
 #define PL_SCX_invlist		(my_vars->GSCX_invlist)