Add a selection of private headers to the secp256k1 package (#35)

https://github.com/XRPLF/mpt-crypto library uses some private headers of
secp256k1.
So, I copy them (and their dependencies) to `include/private`.

This allows conan to be used for secp256k1 library

Author: mathbunnyru

recipes/secp256k1/all/conanfile.py

@@ -1,6 +1,7 @@
 from conan import ConanFile, tools
 from conan.tools.cmake import CMake, CMakeDeps, CMakeToolchain, cmake_layout
-from conan.tools.files import get
+from conan.tools.files import get, copy
+import os
 
 required_conan_version = ">=2.0.0"
 
@@ -44,6 +45,17 @@ def package(self):
         cmake = CMake(self)
         cmake.install()
 
+        # These headers are used by XRPLF/mpt-crypto which is why we need to package them.
+        src_headers = ["util.h", "int128.h", "int128_impl.h", "scalar.h", "scalar_impl.h"]
+        src_headers_dependencies = ["checkmem.h", "int128_native.h", "int128_native_impl.h", "scalar_4x64.h", "scalar_4x64_impl.h", "modinv64.h", "modinv64_impl.h"]
+        for header in src_headers + src_headers_dependencies:
+            copy(
+                self,
+                header,
+                src=os.path.join(self.source_folder, "src"),
+                dst=os.path.join(self.package_folder, "include", "private")
+            )
+
     def package_info(self):
         self.cpp_info.libs = ["secp256k1"]
         self.cpp_info.set_property("cmake_file_name", "secp256k1")