OSS-Fuzz: Require static libraries

Refer to
https://google.github.io/oss-fuzz/further-reading/fuzzer-environment/#runtime-dependencies
for the reasons why this is necessary.
diff --git a/fuzz/CMakeLists.txt b/fuzz/CMakeLists.txt
index 60ff5dc..65675f9 100644
--- a/fuzz/CMakeLists.txt
+++ b/fuzz/CMakeLists.txt
@@ -1,3 +1,6 @@
+if(NOT ENABLE_STATIC)
+  message(FATAL_ERROR "Fuzz targets require static libraries.")
+endif()
 if(NOT WITH_TURBOJPEG)
   message(FATAL_ERROR "Fuzz targets require the TurboJPEG API library.")
 endif()
@@ -24,11 +27,7 @@
 
 macro(add_fuzz_target target source_file)
   add_executable(${target}_fuzzer ${source_file})
-  if(NOT ENABLE_SHARED)
-    target_link_libraries(${target}_fuzzer ${FUZZ_LIBRARY} turbojpeg-static)
-  else()
-    target_link_libraries(${target}_fuzzer ${FUZZ_LIBRARY} turbojpeg)
-  endif()
+  target_link_libraries(${target}_fuzzer ${FUZZ_LIBRARY} turbojpeg-static)
   install(TARGETS ${target}_fuzzer RUNTIME DESTINATION ${FUZZ_BINDIR})
 endmacro()