gh-38931: OS X: do not use -ld_classic
    
Recent versions of Xcode have deprecated `-ld_classic`, so (a) we stop
using it, (b) we filter warnings about it when doctesting, and (c) we
filter some other warnings related to ld in Xcode.

Without these changes, when building with the latest Xcode, I get many
doctest failures because of the new warning
```
ld: warning: -ld_classic is deprecated and will be removed in a future
release
```

### 📝 Checklist

<!-- Put an `x` in all the boxes that apply. -->

- [X] The title is concise and informative.
- [X] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - #12345: short description why this is a dependency -->
<!-- - #34567: ... -->
    
URL: #38931
Reported by: John H. Palmieri
Reviewer(s): Marc Culler

Author: Release Manager

src/bin/sage-env

@@ -383,12 +383,15 @@ if [ -n "$SAGE_LOCAL" ]; then
        # "Toolchains/XcodeDefault.xctoolchain/usr/bin/".  (See #37237.)
        if [ -z "$LD" ]; then
 	   # Running xcode-select on a system with no toolchain writes an
-	   # error message to stderr, so redirect stderr to /dev/null. 
+	   # error message to stderr, so redirect stderr to /dev/null.
 	   XCODE_PATH=$(/usr/bin/xcode-select -p 2> /dev/null)
 	   if [ -n $XCODE_PATH ]; then
                if [ -x "$XCODE_PATH/usr/bin/ld-classic" -o \
 		       -x "$XCODE_PATH/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld-classic" ]; then
-		   LDFLAGS="$LDFLAGS -Wl,-ld_classic"
+                   # Add -ld_classic only if -ld_classic is not deprecated.
+                   if [ -z "$(ld -ld_classic 2>&1 | grep 'ld_classic is deprecated')" ]; then
+		       LDFLAGS="$LDFLAGS -Wl,-ld_classic"
+                   fi
                fi
            else
                # On a macOS system with no toolchain we don't want this script

src/sage/doctest/parsing.py

@@ -1516,6 +1516,21 @@ def do_fixup(self, want, got):
             pythran_numpy_warning_regex = re.compile(r'WARNING: Overriding pythran description with argspec information for: numpy\.random\.[a-z_]+')
             got = pythran_numpy_warning_regex.sub('', got)
             did_fixup = True
+
+        if "ld_classic is deprecated" in got:
+            # New warnings as of Oct '24, Xcode 16.
+            ld_warn_regex = re.compile("ld: warning: -ld_classic is deprecated and will be removed in a future release")
+            got = ld_warn_regex.sub('', got)
+            did_fixup = True
+
+        if "duplicate libraries" in got:
+            # New warnings as of Sept '23, OS X 13.6, new command-line
+            # tools. In particular, these seem to come from ld in
+            # Xcode 15.
+            dup_lib_regex = re.compile("ld: warning: ignoring duplicate libraries: .*")
+            got = dup_lib_regex.sub('', got)
+            did_fixup = True
+
         return did_fixup, want, got
 
     def output_difference(self, example, got, optionflags):

src/sage/tests/cmdline.py

@@ -776,4 +776,13 @@ def test_executable(args, input='', timeout=100.0, pydebug_ignore_warnings=False
                 p.stderr.close()
             err.append(s)
 
-    return (''.join(out), ''.join(err), p.wait())
+    # In case out or err contains a quoted string, force the use of
+    # double quotes so that the output is enclosed in single
+    # quotes. This avoids some doctest failures with some versions of
+    # OS X and Xcode.
+    out = ''.join(out)
+    out = out.replace("'", '"')
+    err = ''.join(err)
+    err = err.replace("'", '"')
+
+    return (out, err, p.wait())