Backport in 1.3.6 some build improvements of 1.3.7:
* link to libm
* usage of find_package to discover Ogg and link with Ogg:ogg target

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,6 +4,7 @@ project(vorbis)
 # Required modules
 include(GNUInstallDirs)
 include(CheckIncludeFiles)
+include(CheckLibraryExists)
 
 # Build options
 option(BUILD_SHARED_LIBS "Build shared library" OFF)
@@ -52,18 +53,12 @@ endfunction()
 
 message(STATUS "Configuring ${PROJECT_NAME} ${PROJECT_VERSION}")
 
+# Find math library
+
+check_library_exists(m floor "" HAVE_LIBM)
+
 # Find ogg dependency
-if(NOT OGG_ROOT)
-    find_package(PkgConfig QUIET)
-    pkg_check_modules(PC_OGG QUIET ogg)
-    find_path(OGG_INCLUDE_DIRS NAMES ogg/ogg.h HINTS ${PC_OGG_INCLUDE_DIRS} PATH_SUFFIXES ogg)
-    find_library(OGG_LIBRARIES NAMES ogg HINTS ${PC_OGG_LIBRARY_DIRS})
-else()
-    find_path(OGG_INCLUDE_DIRS NAMES ogg/ogg.h HINTS ${OGG_ROOT}/include PATH_SUFFIXES ogg)
-    find_library(OGG_LIBRARIES NAMES ogg HINTS ${OGG_ROOT}/lib ${OGG_ROOT}/lib64)
-endif()
-include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(OGG DEFAULT_MSG OGG_INCLUDE_DIRS OGG_LIBRARIES)
+find_package(Ogg REQUIRED)
 
 add_subdirectory(lib)
 
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -83,9 +83,12 @@ if (NOT BUILD_FRAMEWORK)
     get_version_info(VORBISFILE_VERSION_INFO "VF_LIB_CURRENT" "VF_LIB_AGE" "VF_LIB_REVISION")
     set_target_properties(vorbisfile PROPERTIES SOVERSION ${VORBISFILE_VERSION_INFO})
 
-    target_link_libraries(vorbis ${OGG_LIBRARIES})
-    target_link_libraries(vorbisenc ${OGG_LIBRARIES} vorbis)
-    target_link_libraries(vorbisfile ${OGG_LIBRARIES} vorbis)
+    target_link_libraries(vorbis
+        PUBLIC Ogg::ogg
+        PRIVATE $<$<BOOL:${HAVE_LIBM}>:m>
+    )
+    target_link_libraries(vorbisenc PUBLIC vorbis)
+    target_link_libraries(vorbisfile PUBLIC vorbis)
 
     install(FILES ${VORBIS_PUBLIC_HEADERS} DESTINATION ${CMAKE_INSTALL_FULL_INCLUDEDIR}/vorbis)