configure: Use cppflags check helper functions where appropriate

configure

@@ -3774,18 +3774,12 @@ add_cppflags -D_ISOC99_SOURCE
 
 # some compilers silently accept -std=c11, so we also need to check that the
 # version macro is defined properly
-if test_cflags_cpp -std=c11 "__STDC_VERSION__ >= 201112L"; then
-    add_cflags -std=c11
-else
+check_cpp_condition stdlib.h  "__STDC_VERSION__ >= 201112L" -std=c11 &&
+    add_cflags -std=c11 ||
     check_cflags -std=c99
-fi
 
-check_cc -D_FILE_OFFSET_BITS=64 <<EOF && add_cppflags -D_FILE_OFFSET_BITS=64
-#include <stdlib.h>
-EOF
-check_cc -D_LARGEFILE_SOURCE <<EOF && add_cppflags -D_LARGEFILE_SOURCE
-#include <stdlib.h>
-EOF
+check_cppflags -D_FILE_OFFSET_BITS=64
+check_cppflags -D_LARGEFILE_SOURCE
 
 add_host_cppflags -D_ISOC99_SOURCE
 check_host_cflags -std=c99