replace B::COP::stashflags by B::COP::stashlen

6379d4a (between 5.15.9 and 5.16.0) broke B::COP::stashflags which was added
in 5.15.4.

ext/B/B.pm

@@ -15,7 +15,7 @@ require Exporter;
 # walkoptree comes from B.xs
 
 BEGIN {
-    $B::VERSION = '1.34';
+    $B::VERSION = '1.35';
     @B::EXPORT_OK = ();
 
     # Our BOOT code needs $VERSION set, and will append to @EXPORT_OK.
@@ -1211,7 +1211,7 @@ Only when perl was compiled with ithreads.
 
 =item stashpv
 
-=item stashflags
+=item stashlen
 
 =item file
 

ext/B/B.xs

@@ -1227,8 +1227,8 @@ pv(o)
 	    ST(0) = newSVpvn_flags(o->op_pv, strlen(o->op_pv), SVs_TEMP);
 
 #define COP_label(o)	CopLABEL(o)
-#ifdef CopSTASH_flags
-#define COP_stashflags(o)	CopSTASH_flags(o)
+#ifdef CopSTASH_len
+#define COP_stashlen(o)	CopSTASH_len(o)
 #endif
 
 MODULE = B	PACKAGE = B::COP		PREFIX = COP_
@@ -1253,10 +1253,10 @@ COP_stash(o)
 	PUSHs(make_sv_object(aTHX_
 			     ix ? (SV *)CopFILEGV(o) : (SV *)CopSTASH(o)));
 
-#ifdef CopSTASH_flags
+#ifdef CopSTASH_len
 
 U32
-COP_stashflags(o)
+COP_stashlen(o)
 	B::COP	o
 
 #endif