HDFS-14394: Add -std=c99 / -std=gnu99 to libhdfs compile flags

Signed-off-by: Todd Lipcon <todd@apache.org>

hadoop-common-project/hadoop-common/HadoopCommon.cmake

@@ -193,7 +193,6 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
 elseif(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
     # Solaris flags. 64-bit compilation is mandatory, and is checked earlier.
     hadoop_add_compiler_flags("-m64 -D_POSIX_C_SOURCE=200112L -D__EXTENSIONS__ -D_POSIX_PTHREAD_SEMANTICS")
-    set(CMAKE_C_FLAGS "-std=gnu99 ${CMAKE_C_FLAGS}")
     set(CMAKE_CXX_FLAGS "-std=gnu++98 ${CMAKE_CXX_FLAGS}")
     hadoop_add_linker_flags("-m64")
 
@@ -211,3 +210,6 @@ elseif(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
         message(FATAL_ERROR "Unrecognised CMAKE_SYSTEM_PROCESSOR ${CMAKE_SYSTEM_PROCESSOR}")
     endif()
 endif()
+
+# Set GNU99 as the C standard to use
+set(CMAKE_C_FLAGS "-std=gnu99 ${CMAKE_C_FLAGS}")