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.