libuv: Compile as C 90 on Solaris 5.10 with SunPro 5.14

Utilities/cmlibuv/CMakeLists.txt

@@ -221,12 +221,14 @@ if(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
     __EXTENSIONS__
     )
   if(CMAKE_SYSTEM_VERSION STREQUAL "5.10")
+    set(CMAKE_C_STANDARD 90)
+    if(CMAKE_VERSION VERSION_LESS 3.8.20170504 AND CMAKE_C_COMPILER_ID STREQUAL "SunPro" AND NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 5.14)
+      # The running version of CMake does not know how to add this flag.
+      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c90")
+    endif()
     list(APPEND uv_defines
       _XOPEN_SOURCE=500
       )
-    if(CMAKE_C_STANDARD)
-      set(CMAKE_C_STANDARD 90)
-    endif()
   else()
     list(APPEND uv_defines
       _XOPEN_SOURCE=600