chore: initialize build2 project

cpm/.gitignore

@@ -0,0 +1,5 @@
+cpm
+
+# Testscript output directory (can be symlink).
+#
+test-cpm

cpm/buildfile

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+libs =
+#import libs += libhello%lib{hello}
+
+exe{cpm}: {hxx ixx txx cxx}{**} $libs testscript
+
+cxx.poptions =+ "-I$out_root" "-I$src_root"

cpm/cpm.cxx

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+#include <iostream>
+
+int main (int argc, char* argv[])
+{
+  using namespace std;
+
+  if (argc < 2)
+  {
+    cerr << "error: missing name" << endl;
+    return 1;
+  }
+
+  cout << "Hello, " << argv[1] << '!' << endl;
+}

cpm/testscript

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+: basics
+:
+$* 'World' >'Hello, World!'
+
+: missing-name
+:
+$* 2>>EOE != 0
+error: missing name
+EOE