Solaris: disable deprecated SHOPT_PFSH by default

Solaris /bin/ksh disables the SHOPT_PFSH compile option ("solaris
exec_attr(4) profile execution") with a patch. Since this option
applies to Solaris and variants only, let's upstream that change.

(Solaris now provides pfksh93 as a wrapper around ksh93, and does
the same for other shells, so profiling functionality is no longer
ksh-specific.)

If you want to re-enable it, add -DSHOPT_PFSH to your $CCFLAGS.

Original patch:
https://github.com/oracle/solaris-userland/blob/master/components/ksh93/patches/150-CR7168611.patch

src/cmd/ksh93/Makefile:
- Add note that edits in Makefile are ineffective as we do not ship
  nmake.
- Disable SHOPT_PFSH, cosmetically.

src/cmd/ksh93/Mamfile:
- Remove -DSHOPT_PFSH from all compiler commands.

src/cmd/ksh93/Makefile

@@ -1,5 +1,9 @@
 /*
  * ksh makefile
+ *
+ * NOTE: since ksh 93u+m does not use/include nmake for various reasons,
+ * any changes here are ineffective and this is for reference only. Edit
+ * Mamfile instead (though it might still be good to update this too).
  */
 
 SH := $(PWD:B:/[0-9]*$//:N=ksh*:-ksh)		/* name of the shell program */
@@ -37,7 +41,7 @@ SHOPT_MULTIBYTE == 1		/* multibyte character handling */
 SHOPT_NAMESPACE == 1		/* allow namespaces */
 SHOPT_OLDTERMIO ==		/* support both TCGETA and TCGETS */
 SHOPT_OPTIMIZE == 1		/* optimize loop invariants */
-SHOPT_PFSH == 1			/* solaris exec_attr(4) profile execution */
+SHOPT_PFSH == 0			/* solaris exec_attr(4) profile execution */
 SHOPT_P_SUID ==			/* real uid's that require -p for set[ug]id */
 SHOPT_RAWONLY == 1		/* make viraw the only vi mode */
 SHOPT_REGRESS ==		/* enable __regress__ builtin and instrumented intercepts for testing */