Merge bitcoin-core/secp256k1#1422: cmake: Install libsecp256k1.pc file

421d84855a ci: Align Autotools/CMake `CI_INSTALL` directory names (Hennadii Stepanov)
9f005c60d6 cmake: Install `libsecp256k1.pc` file (Hennadii Stepanov)

Pull request description:

  This PR allows downstream projects to use pkg-config to search for the libsecp256k1 library that is built with CMake.

  Addressed https://github.com/bitcoin-core/secp256k1/discussions/1419#discussioncomment-6922896:
  > We could just ship the pkg-config file also in CMake builds.

ACKs for top commit:
  real-or-random:
    ACK 421d84855a I compared the generated pc files and they match in autotools and CMake

Tree-SHA512: 8e54eb7c76bc727ab18715258c06cc2a419c6c04892a2bd7bfe34392f9a3223f673ff84d2d21b00b3c222b357f02296ec49c872532d98ea0a2f17ef1ed6b6ac1

.github/workflows/ci.yml

@@ -792,7 +792,7 @@ jobs:
 
       - name: Check installation with Autotools
         env:
-          CI_INSTALL: ${{ runner.temp }}/${{ github.run_id }}${{ github.action }}
+          CI_INSTALL: ${{ runner.temp }}/${{ github.run_id }}${{ github.action }}/install
         run: |
           ./autogen.sh && ./configure --prefix=${{ env.CI_INSTALL }} && make clean && make install && ls -RlAh ${{ env.CI_INSTALL }}
           gcc -o ecdsa examples/ecdsa.c $(PKG_CONFIG_PATH=${{ env.CI_INSTALL }}/lib/pkgconfig pkg-config --cflags --libs libsecp256k1) -Wl,-rpath,"${{ env.CI_INSTALL }}/lib" && ./ecdsa

cmake/GeneratePkgConfigFile.cmake

@@ -0,0 +1,8 @@
+function(generate_pkg_config_file in_file)
+  set(prefix ${CMAKE_INSTALL_PREFIX})
+  set(exec_prefix \${prefix})
+  set(libdir \${exec_prefix}/${CMAKE_INSTALL_LIBDIR})
+  set(includedir \${prefix}/${CMAKE_INSTALL_INCLUDEDIR})
+  set(PACKAGE_VERSION ${PROJECT_VERSION})
+  configure_file(${in_file} ${PROJECT_NAME}.pc @ONLY)
+endfunction()

src/CMakeLists.txt

@@ -162,4 +162,12 @@ if(SECP256K1_INSTALL)
       ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}-config-version.cmake
     DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}
   )
+
+  include(GeneratePkgConfigFile)
+  generate_pkg_config_file(${PROJECT_SOURCE_DIR}/libsecp256k1.pc.in)
+  install(
+    FILES
+      ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc
+    DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig
+  )
 endif()