configure: Drop obsolete check for the alloc_size attribute

We recently bumped our requirement for Clang to at least version 6.0.
And according to:

 https://releases.llvm.org/6.0.0/tools/clang/docs/AttributeReference.html

Clang v6.0 supports the alloc_size attribute. Thus we can drop this
check in the configure script now.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210714072855.785566-1-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/configure b/configure
index 63f38fa..026704f 100755 (executable)
--- a/configure
+++ b/configure
@@ -3266,18 +3266,6 @@ if ! compile_prog "$glib_cflags" "$glib_libs" ; then
               "build target"
 fi
 
-# Silence clang 3.5.0 warnings about glib attribute __alloc_size__ usage
-cat > $TMPC << EOF
-#include <glib.h>
-int main(void) { return 0; }
-EOF
-if ! compile_prog "$glib_cflags -Werror" "$glib_libs" ; then
-    if cc_has_warning_flag "-Wno-unknown-attributes"; then
-        glib_cflags="-Wno-unknown-attributes $glib_cflags"
-        CONFIGURE_CFLAGS="-Wno-unknown-attributes $CONFIGURE_CFLAGS"
-    fi
-fi
-
 # Silence clang warnings triggered by glib < 2.57.2
 cat > $TMPC << EOF
 #include <glib.h>