darwin, configuration, check properly for dwarf2 debug line support

This corrects a long-standing misconfiguration for Darwin.
The assembler supports the “.file” and “.loc” directives, but
the GCC configury was not detecting this because it was 
using objdump, which does not exist on most Darwin installations.

We added support for “otool” to GCC and now we can use that to
make the check that’s done with objdump on ELF targets.

2018-12-24  Iain Sandoe  <iain@sandoe.co.uk>

	* configure.ac (dwarf2_debug_line): Check for the debug_line
	section using otool when there’s no objdump available.
	* configure: Regenerate.

From-SVN: r267393

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2018-12-24  Iain Sandoe  <iain@sandoe.co.uk>
+
+	* configure.ac (dwarf2_debug_line): Check for the debug_line
+	section using otool when there’s no objdump available.
+	* configure: Regenerate.
+
 2018-12-24  Jan Hubicka  <hubicka@ucw.cz>
 
 	* ipa-utils.c (ipa_merge_profiles): Fix updating of fnsummary;

gcc/configure

@@ -27724,6 +27724,10 @@ fi
    && $gcc_cv_objdump -h conftest.o 2> /dev/null \
       | grep debug_line > /dev/null 2>&1; then
      gcc_cv_as_dwarf2_debug_line=yes
+   elif test x$gcc_cv_otool != x \
+   && $gcc_cv_otool -l conftest.o 2> /dev/null \
+      | grep debug_line > /dev/null 2>&1; then
+     gcc_cv_as_dwarf2_debug_line=yes
    fi
     else
       echo "configure: failed program was" >&5

gcc/configure.ac

@@ -4926,6 +4926,10 @@ if test x"$insn" != x; then
    && $gcc_cv_objdump -h conftest.o 2> /dev/null \
       | grep debug_line > /dev/null 2>&1; then
      gcc_cv_as_dwarf2_debug_line=yes
+   elif test x$gcc_cv_otool != x \
+   && $gcc_cv_otool -l conftest.o 2> /dev/null \
+      | grep debug_line > /dev/null 2>&1; then
+     gcc_cv_as_dwarf2_debug_line=yes
    fi])
 
 # The .debug_line file table must be in the exact order that