GenPkgConfig.cmake: fix windows case and add comments

modules/GenPkgConfig.cmake

@@ -97,8 +97,10 @@ macro(gpc_convert_libstyle_to_pkgconfig _liblist)
   # Convert to pkg-config file format
   set(${_liblist}_CPY "${${_liblist}}")
   set(${_liblist} "")
+  # we consider a list of libraries as input
   foreach(_dep ${${_liblist}_CPY})
-    if (${_dep} MATCHES "^/")
+    if (${_dep} MATCHES "^/|^[A-Z]:/")
+      # case library is an absolute path (e.g. /opt/foo/lib/libfoo.so)
       get_filename_component(dep_libname ${_dep} NAME)
       get_filename_component(dep_libdir  ${_dep} PATH)
       foreach( _ext ${CMAKE_FIND_LIBRARY_SUFFIXES} )
@@ -106,10 +108,12 @@ macro(gpc_convert_libstyle_to_pkgconfig _liblist)
       endforeach()
       string(REGEX REPLACE "^lib" "" dep_libname "${dep_libname}")
       list(APPEND ${_liblist} -L${dep_libdir} -l${dep_libname})
-    elseif(NOT ${_dep} MATCHES "^-")
-      list(APPEND ${_liblist} "-l${_dep}")
-    else()
+    elseif(${_dep} MATCHES "^-l")
+      # case library given with -l (e.g. -lfoo)
       list(APPEND ${_liblist} ${_dep})
+    else()
+      # case library given by name (e.g. foo)
+      list(APPEND ${_liblist} "-l${_dep}")
     endif()
   endforeach()
 endmacro(gpc_convert_libstyle_to_pkgconfig)