testsuite: Add tests for system-cxx-std-lib package

Test that we can successfully link against C++ code both in GHCi and
batch compilation.

See #20010

testsuite/tests/package/T20010/Makefile

+TOP=../../../..
+include $(TOP)/mk/boilerplate.mk
+include $(TOP)/mk/test.mk
+
+T20010:
+	'$(TEST_HC)' $(TEST_HC_OPTS) -c T20010.hs
+	'$(TEST_HC)' $(TEST_HC_OPTS) -c T20010_c.cpp
+	'$(TEST_HC)' $(TEST_HC_OPTS) -package system-cxx-std-lib T20010_c.o T20010.o -o T20010
+	./T20010
+
+T20010-ghci:
+	'$(TEST_HC)' $(TEST_HC_OPTS) -c T20010.hs
+	# We must build with PIC lest we end up with R_X86_64_32 relocations in
+	# .rodata which precludes linking into a shared object and therefore loading
+	# in GHCi
+	'$(TEST_HC)' $(TEST_HC_OPTS) -c -fPIC T20010_c.cpp
+	'$(TEST_HC)' $(TEST_HC_OPTS_INTERACTIVE) -package system-cxx-std-lib T20010_c.o <T20010-ghci.script
+

testsuite/tests/package/T20010/T20010-ghci.script

+:load T20010
+hello 42

testsuite/tests/package/T20010/T20010-ghci.stdout

+hello world 42

testsuite/tests/package/T20010/T20010.hs

+module Main where
+
+import Foreign.C.Types
+
+foreign import ccall unsafe "hello" hello :: CInt -> IO ()
+
+main :: IO ()
+main = do
+    hello 42
+

testsuite/tests/package/T20010/T20010.stdout

+hello world 42

testsuite/tests/package/T20010/T20010_c.cpp

+#include <iostream>
+
+extern "C" {
+void hello(int x) {
+    std::cout << "hello world " << x << std::endl;
+}
+}

testsuite/tests/package/T20010/all.T

+# Test that GHC links to the C++ standard library as expected
+# when the system-cxx-std-lib package is used.
+test('T20010', normal, makefile_test, [])
+test('T20010-ghci', extra_files(['T20010_c.cpp', 'T20010.hs']), makefile_test, [])