cmake: fix build failure when git repo is initialized but no first commit

Closes https://github.com/espressif/esp-idf/issues/3920

tools/cmake/project.cmake

@@ -38,8 +38,9 @@ function(__project_get_revision var)
             if(PROJECT_VER_GIT)
                 set(PROJECT_VER ${PROJECT_VER_GIT})
             else()
-                message(STATUS "Project is not inside a git repository, \
-                        will not use 'git describe' to determine PROJECT_VER.")
+                message(STATUS "Project is not inside a git repository, or git repository has no commits;"
+                        " will not use 'git describe' to determine PROJECT_VER.")
+                set(PROJECT_VER 1)
             endif()
         endif()
     endif()

tools/cmake/third_party/GetGitRevisionDescription.cmake.in

@@ -24,10 +24,12 @@ if(HEAD_CONTENTS MATCHES "ref")
 	if(EXISTS "@GIT_DIR@/${HEAD_REF}")
 		configure_file("@GIT_DIR@/${HEAD_REF}" "@GIT_DATA@/head-ref" COPYONLY)
 	else()
-		configure_file("@GIT_DIR@/packed-refs" "@GIT_DATA@/packed-refs" COPYONLY)
-		file(READ "@GIT_DATA@/packed-refs" PACKED_REFS)
-		if(${PACKED_REFS} MATCHES "([0-9a-z]*) ${HEAD_REF}")
-			set(HEAD_HASH "${CMAKE_MATCH_1}")
+		if(EXISTS "@GIT_DIR@/packed-refs")
+			configure_file("@GIT_DIR@/packed-refs" "@GIT_DATA@/packed-refs" COPYONLY)
+			file(READ "@GIT_DATA@/packed-refs" PACKED_REFS)
+			if(${PACKED_REFS} MATCHES "([0-9a-z]*) ${HEAD_REF}")
+				set(HEAD_HASH "${CMAKE_MATCH_1}")
+			endif()
 		endif()
 	endif()
 else()