Pass C compiler and pkg-config to subprojects (#345)

Co-authored-by: Helmut Grohne <[email protected]>

Author: sebastinas

CMakeLists.txt

@@ -46,11 +46,13 @@ ExternalProject_Add(BearSource
         CMAKE_ARGS
             -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
             -DCMAKE_PROJECT_VERSION=${CMAKE_PROJECT_VERSION}
+            -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
             -DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD}
             -DCMAKE_CXX_STANDARD_REQUIRED=${CMAKE_CXX_STANDARD_REQUIRED}
             -DCMAKE_CXX_EXTENSIONS=${CMAKE_CXX_EXTENSIONS}
             -DCMAKE_CXX_FLAGS:STRING=${CMAKE_CXX_FLAGS}
             -DCMAKE_CXX_COMPILER:STRING=${CMAKE_CXX_COMPILER}
+            -DPKG_CONFIG_EXECUTABLE:PATH=${PKG_CONFIG_EXECUTABLE}
         CMAKE_CACHE_ARGS
             -DCMAKE_PREFIX_PATH:PATH=${CMAKE_PREFIX_PATH}
             -DCMAKE_INSTALL_PREFIX:PATH=${STAGED_INSTALL_PREFIX}