getopt: Fix compilation settings

INTERFACE doesn't define the symbol when compiling the library itself.
PUBLIC should be used when the definition is needed both by the library
and by the users.

externals/getopt/CMakeLists.txt

@@ -7,5 +7,5 @@ set(HEADERS
 
 create_directory_groups(${SRCS} ${HEADERS})
 add_library(getopt ${SRCS} ${HEADERS})
-target_compile_definitions(getopt INTERFACE STATIC_GETOPT)
+target_compile_definitions(getopt PUBLIC STATIC_GETOPT)
 target_include_directories(getopt INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})