[lldb][dotest] Add `#include <algorithm>` to libc++ detection

[rupprecht]

Summary

Speculative fix after 34ef51b5f979 broke the lldb buildbot on libc++ tests.

[merge_guards_bot]

Unit tests: pass. 60743 tests passed, 0 failed and 726 were skipped.

clang-format: pass.

Build artifacts: console-log.txt, CMakeCache.txt, test-results.xml, diff.json

lldb/packages/Python/lldbsuite/test/dotest.py

if lldbplatformutil.target_is_android() or lldbplatformutil.platformIsDarwin():
         return True, "libc++ always present"
 
     if platform == "linux":
         if os.path.isdir("/usr/include/c++/v1"):
             return True, "Headers found, let's hope they work"
         with tempfile.NamedTemporaryFile() as f:
             cmd = [configuration.compiler, "-xc++", "-stdlib=libc++", "-o", f.name, "-"]
             p = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True)
-            _, stderr = p.communicate("int main() {}")
+            _, stderr = p.communicate("#include <algorithm>\nint main() {}")
             if not p.returncode:
                 return True, "Compiling with -stdlib=libc++ works"
             return False, "Compiling with -stdlib=libc++ fails with the error: %s" % stderr
 
     return False, "Don't know how to build with libc++ on %s" % platform
 
 def checkLibcxxSupport():
     result, reason = canRunLibcxxTests()