Revert "switch removal: no need for -DM anymore"

This reverts commit 18b5dc4.

perl.c

@@ -3639,7 +3639,7 @@ Perl_get_debug_opts(pTHX_ const char **s, bool givehelp)
          * impacting the definitions of all the other flags in perl.h
          * However because the logic is guarded by isWORDCHAR we can
          * fill in holes with non-wordchar characters instead. */
-        static const char debopts[] = "psltocPmfrxuUhXDSTRJvCAq BLiy";
+        static const char debopts[] = "psltocPmfrxuUhXDSTRJvCAqMBLiy";
 
         for (; isWORDCHAR(**s); (*s)++) {
             const char * const d = strchr(debopts,**s);

perl.h

@@ -4827,12 +4827,12 @@ Gid_t getegid (void);
 #define DEBUG_C_FLAG		0x00200000 /*2097152 */
 #define DEBUG_A_FLAG		0x00400000 /*4194304 */
 #define DEBUG_q_FLAG		0x00800000 /*8388608 */
-/* was smartmatch, now free     0x01000000  16777216 */
+#define DEBUG_M_FLAG		0x01000000 /*16777216*/
 #define DEBUG_B_FLAG		0x02000000 /*33554432*/
 #define DEBUG_L_FLAG		0x04000000 /*67108864*/
 #define DEBUG_i_FLAG		0x08000000 /*134217728*/
 #define DEBUG_y_FLAG		0x10000000 /*268435456*/
-#define DEBUG_MASK		0x1EFFEFFF /* mask of all the standard flags */
+#define DEBUG_MASK		0x1FFFEFFF /* mask of all the standard flags */
 
 #define DEBUG_DB_RECURSE_FLAG	0x40000000
 #define DEBUG_TOP_FLAG		0x80000000 /* -D was given --> PL_debug |= FLAG */
@@ -4866,6 +4866,7 @@ Gid_t getegid (void);
 #  define DEBUG_C_TEST_ UNLIKELY(PL_debug & DEBUG_C_FLAG)
 #  define DEBUG_A_TEST_ UNLIKELY(PL_debug & DEBUG_A_FLAG)
 #  define DEBUG_q_TEST_ UNLIKELY(PL_debug & DEBUG_q_FLAG)
+#  define DEBUG_M_TEST_ UNLIKELY(PL_debug & DEBUG_M_FLAG)
 #  define DEBUG_B_TEST_ UNLIKELY(PL_debug & DEBUG_B_FLAG)
 
 /* Locale initialization comes earlier than PL_debug gets set,
@@ -4912,6 +4913,7 @@ Gid_t getegid (void);
 #  define DEBUG_C_TEST DEBUG_C_TEST_
 #  define DEBUG_A_TEST DEBUG_A_TEST_
 #  define DEBUG_q_TEST DEBUG_q_TEST_
+#  define DEBUG_M_TEST DEBUG_M_TEST_
 #  define DEBUG_B_TEST DEBUG_B_TEST_
 #  define DEBUG_L_TEST DEBUG_L_TEST_
 #  define DEBUG_i_TEST DEBUG_i_TEST_
@@ -5010,6 +5012,7 @@ Gid_t getegid (void);
 #  define DEBUG_C(a) DEBUG__(DEBUG_C_TEST, a)
 #  define DEBUG_A(a) DEBUG__(DEBUG_A_TEST, a)
 #  define DEBUG_q(a) DEBUG__(DEBUG_q_TEST, a)
+#  define DEBUG_M(a) DEBUG__(DEBUG_M_TEST, a)
 #  define DEBUG_B(a) DEBUG__(DEBUG_B_TEST, a)
 #  define DEBUG_L(a) DEBUG__(DEBUG_L_TEST, a)
 #  define DEBUG_i(a) DEBUG__(DEBUG_i_TEST, a)
@@ -5041,6 +5044,7 @@ Gid_t getegid (void);
 #  define DEBUG_C_TEST (0)
 #  define DEBUG_A_TEST (0)
 #  define DEBUG_q_TEST (0)
+#  define DEBUG_M_TEST (0)
 #  define DEBUG_B_TEST (0)
 #  define DEBUG_L_TEST (0)
 #  define DEBUG_i_TEST (0)
@@ -5076,6 +5080,7 @@ Gid_t getegid (void);
 #  define DEBUG_C(a)
 #  define DEBUG_A(a)
 #  define DEBUG_q(a)
+#  define DEBUG_M(a)
 #  define DEBUG_B(a)
 #  define DEBUG_L(a)
 #  define DEBUG_i(a)

pod/perlrun.pod

@@ -432,6 +432,7 @@ B<-D14> is equivalent to B<-Dtls>):
    4194304  A  Consistency checks on internal structures
    8388608  q  quiet - currently only suppresses the "EXECUTING"
                message
+  16777216  M  trace smart match resolution
   33554432  B  dump suBroutine definitions, including special
                Blocks like BEGIN
   67108864  L  trace Locale-related info; what gets output is very