Fix build on Solaris 11.4 (re: d3cd4cf)

It was working on Solaris 11.3, but there were still problems
building on Solaris 11.4 with GCC (as on the evaluation VM
downloaded directly from Oracle):
1. ksh immediately segfaulted. Experimenting with the compiler
   flags Oracle uses revealed that we need to define _XPG6 for ksh
   not to segfault. Why is a mystery.
2. The default path logic used by 'command -p' and the 'getconf
   PATH' builtin command was still broken: the result did not
   include any of the /usr/xpg?/bin directories where the standard
   POSIX utilities actually live. Testing shows that the result of
   the C language probe 'confstr(_CS_PATH,name,length)' is broken
   on Solaris (it only yields the paths to the historic
   non-standard utilities, defeating the purpose) unless _XPG7 is
   defined; but the latter makes ksh segfault again. So another
   solution is needed.

src/cmd/INIT/package.sh, bin/package:
- Add another hack to add the -D_XPG6 flag to CCFLAGS if we're
  running SunOS aka Solaris. (I've tried to add a 'cc.sol11' script
  to src/cmd/INIT/ instead, but for some reason that I just don't
  have time to figure out, the INIT system ignores that on Solaris
  with gcc, so this is the only way I could come up with. Any
  patches for less hacky alternatives would be welcome.)

src/lib/libast/comp/conf.sh:
- Sanitise the code for finding the best 'getconf' utility.

src/lib/libast/comp/conf.tab: PATH:
- Since the C-languge getconf(_CS_PATH,...) is broken on Solaris
  11.4, replace the C language probe with a shell script probe that
  uses the external 'getconf' utility.
- To avoid ksh overriding the result of this probe with the result
  of its own getconf(_CS_PATH,...) call, which would make Solaris
  use the wrong value again, specify this as an AST configuration
  entry instead of a POSIX entry. This should be good enough for
  all systems; the OS 'getconf' utility should be reliable and the
  default path value is constant for each OS, so can be hardcoded.

src/cmd/ksh93/tests/builtins.sh:
- Add another 'sleep .1' to the 'sleep -s 31' test as it was still
  intermittently failing on Solaris and possibly other systems.

bin/package

@@ -5407,6 +5407,17 @@ make|view)
 		esac
 		;;
 	esac
+	# Hack for Solaris 11.4, which needs -D_XPG6 in C flags to not segfault
+	case `uname` in
+	SunOS)	case " $CCFLAGS " in
+		*" -D_XPG6 "*)
+			;;
+		*)	CCFLAGS="-D_XPG6${CCFLAGS:+ $CCFLAGS}"
+			export CCFLAGS
+			;;
+		esac
+		;;
+	esac
 
 	cd $PACKAGEROOT
 	case $package in

src/cmd/INIT/package.sh

@@ -5406,6 +5406,17 @@ make|view)
 		esac
 		;;
 	esac
+	# Hack for Solaris 11.4, which needs -D_XPG6 in C flags to not segfault
+	case `uname` in
+	SunOS)	case " $CCFLAGS " in
+		*" -D_XPG6 "*)
+			;;
+		*)	CCFLAGS="-D_XPG6${CCFLAGS:+ $CCFLAGS}"
+			export CCFLAGS
+			;;
+		esac
+		;;
+	esac
 
 	cd $PACKAGEROOT
 	case $package in

src/cmd/ksh93/tests/builtins.sh

@@ -876,6 +876,7 @@ cat >| "$sleepsig" << 'EOF'
 sleep -s 31 &
 sleep .1
 kill -CONT $!
+sleep .1
 if kill -0 $!; then
 	kill -TERM $! # Don't leave a lingering background process
 	exit 1

src/lib/libast/comp/conf.sh

@@ -344,17 +344,21 @@ for d in \
 	/usr/sbin \
 	/sbin \
 	$PATH
-do	if	test -x $d/getconf
-	then	case `$d/getconf --?-version 2>&1` in
+do	case $d in
+	/*)	;;
+	*)	continue ;;
+	esac
+	if	test -x "$d/getconf"
+	then	case `"$d/getconf" --?-version 2>&1` in
 		*"AT&T"*"Research"*)
 			: presumably an implementation also configured from conf.tab
-			;;
-		*)	CONF_getconf=$d/getconf
-			if	$CONF_getconf -a >/dev/null 2>&1
-			then	CONF_getconf_a=-a
-			fi
+			continue
 			;;
 		esac
+		CONF_getconf=$d/getconf
+		if	"$CONF_getconf" -a >/dev/null 2>&1
+		then	CONF_getconf_a=-a
+		fi
 		break
 	fi
 done

src/lib/libast/comp/conf.tab

@@ -368,22 +368,16 @@ PAGESIZE			POSIX	SC 1 MU		PAGESIZE PAGE_SIZE 4096	cc{
 }
 PAGE_SIZE			POSIX	SC 1 MU		_AST_PAGESIZE
 PASS_MAX			SVID	SC 1 CDLMU	8
-PATH				POSIX	CS 1 MU		cc{
-	#include <stdio.h>
-	#include <unistd.h>
-	int main()
-	{
-		size_t length = confstr(_CS_PATH, 0, 0);
-		if(!length)
-			printf("\\"/bin:/usr/bin\\"");
-		else
-		{
-			char path[length];
-			confstr(_CS_PATH, path, length);
-			printf("\\"%s\\"", path);
-		}
-		return 0;
-	}
+PATH				AST	CS 1 MU		sh{
+	CONF_path=
+	case $CONF_getconf in
+	'')	;;
+	*)	CONF_path=`"$CONF_getconf" PATH` ;;
+	esac
+	case $CONF_path in
+	'')	echo '"/bin:/usr/bin"' ;;
+	*)	echo "\\"$CONF_path\\"" ;;
+	esac
 }
 PATH_MAX			POSIX	PC 1 CDLMUX	MAXPATHLEN 1024
 PBS				POSIX	SC 2 FUW