unit tests: Test that relative install_rpath works correctly

We weren't testing this with C++, so the breakage was missed.

https://github.com/mesonbuild/meson/issues/2814

run_unittests.py

@@ -2288,11 +2288,18 @@ class LinuxlikeTests(BasePlatformTests):
         testdir = os.path.join(self.unit_test_dir, '11 build_rpath')
         self.init(testdir)
         self.build()
+        # C program RPATH
         build_rpath = get_rpath(os.path.join(self.builddir, 'prog'))
         self.assertEqual(build_rpath, '$ORIGIN/sub:/foo/bar')
         self.install()
         install_rpath = get_rpath(os.path.join(self.installdir, 'usr/bin/prog'))
         self.assertEqual(install_rpath, '/baz')
+        # C++ program RPATH
+        build_rpath = get_rpath(os.path.join(self.builddir, 'progcxx'))
+        self.assertEqual(build_rpath, '$ORIGIN/sub:/foo/bar')
+        self.install()
+        install_rpath = get_rpath(os.path.join(self.installdir, 'usr/bin/progcxx'))
+        self.assertEqual(install_rpath, 'baz')
 
     def test_pch_with_address_sanitizer(self):
         testdir = os.path.join(self.common_test_dir, '13 pch')

test cases/unit/11 build_rpath/meson.build

@@ -1,4 +1,4 @@
-project('build rpath', 'c')
+project('build rpath', 'c', 'cpp')
 
 subdir('sub')
 executable('prog', 'prog.c',
@@ -7,3 +7,10 @@ executable('prog', 'prog.c',
   install_rpath : '/baz',
   install : true,
   )
+
+executable('progcxx', 'prog.cc',
+  link_with : l,
+  build_rpath : '/foo/bar',
+  install_rpath : 'baz',
+  install : true,
+  )

test cases/unit/11 build_rpath/prog.cc

@@ -0,0 +1,8 @@
+#include <string>
+#include <iostream>
+
+int main(int argc, char **argv) {
+    std::string* s = new std::string("Hello");
+    delete s;
+    return 0;
+}