cmake, refactor: Move `find_package(Git)` to `src/CMakeLists.txt`

diff --git a/cmake/script/GenerateBuildInfo.cmake b/cmake/script/GenerateBuildInfo.cmake
index d3ee2eb0..694961df 100644
--- a/cmake/script/GenerateBuildInfo.cmake
+++ b/cmake/script/GenerateBuildInfo.cmake
@@ -5,7 +5,7 @@
 macro(fatal_error)
   message(FATAL_ERROR "\n"
     "Usage:\n"
-    "  cmake -D BUILD_INFO_HEADER_PATH=<path> [-D SOURCE_DIR=<path>] -P ${CMAKE_CURRENT_LIST_FILE}\n"
+    "  cmake -D BUILD_INFO_HEADER_PATH=<path> -D GIT_EXECUTABLE=<path> [-D SOURCE_DIR=<path>] -P ${CMAKE_CURRENT_LIST_FILE}\n"
     "All specified paths must be absolute ones.\n"
   )
 endmacro()
@@ -31,8 +31,7 @@ endif()
 set(GIT_TAG)
 set(GIT_COMMIT)
 if(NOT "$ENV{BITCOIN_GENBUILD_NO_GIT}" STREQUAL "1")
-  find_package(Git QUIET)
-  if(Git_FOUND)
+  if(GIT_EXECUTABLE)
     execute_process(
       COMMAND ${GIT_EXECUTABLE} rev-parse --is-inside-work-tree
       WORKING_DIRECTORY ${WORKING_DIR}
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index b37f3c8c..ddbf2d6d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -37,9 +37,10 @@ if(NOT CMAKE_ARCHIVE_OUTPUT_DIRECTORY)
   set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/lib)
 endif()
 
+find_package(Git QUIET)
 add_custom_target(generate_build_info
   BYPRODUCTS ${PROJECT_BINARY_DIR}/src/bitcoin-build-info.h
-  COMMAND ${CMAKE_COMMAND} -DBUILD_INFO_HEADER_PATH=${PROJECT_BINARY_DIR}/src/bitcoin-build-info.h -DSOURCE_DIR=${PROJECT_SOURCE_DIR} -P ${PROJECT_SOURCE_DIR}/cmake/script/GenerateBuildInfo.cmake
+  COMMAND ${CMAKE_COMMAND} -DGIT_EXECUTABLE=${GIT_EXECUTABLE} -DBUILD_INFO_HEADER_PATH=${PROJECT_BINARY_DIR}/src/bitcoin-build-info.h -DSOURCE_DIR=${PROJECT_SOURCE_DIR} -P ${PROJECT_SOURCE_DIR}/cmake/script/GenerateBuildInfo.cmake
   COMMENT "Generating bitcoin-build-info.h"
   VERBATIM
 )