diff -ru isync-1.4.2.orig/configure isync-1.4.2/configure
--- isync-1.4.2.orig/configure	2021-07-16 12:36:23.344522571 +0200
+++ isync-1.4.2/configure	2021-07-16 12:39:20.448517026 +0200
@@ -3978,51 +3978,6 @@
 fi
 
 
-if test "$GCC" = yes; then
-    warnings="
-        -Wall -Wextra
-        -Wshadow
-        -Wcast-qual
-        -Wformat=2 -Wformat-signedness -Wformat-nonliteral
-        -Wstrict-prototypes
-
-        -Wno-overlength-strings
-    "
-    CFLAGS="$CFLAGS -pipe -std=c11 -pedantic $(echo $warnings)"
-fi
-
-
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-
-void fkt(void)
-{
-    int a = 42;  // c99 comment
-
-    for (int i = 0; i < a; i++) {}  // declaration inside for()
-    int b;  // declaration after code
-}
-
-// c11 anonymous structs/unions
-struct base {
-    int a;
-};
-union deriv {
-    struct base gen;
-    struct {
-        int a;
-        int b;
-    };
-};
-
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-
-else
-  as_fn_error $? "compiler does not support required C11 features" "$LINENO" 5
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-
 CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
 
 # Extract the first word of "perl", so it can be a program name with args.