configure: Miscellaneous small changes to helper functions

- Reuse sanitize_var_name() where appropriate
- Add some quotes to enabled()/disabled() to ease readability
- Fix logged names of some helper functions
- Filter LDFLAGS also in test_ldflags()

configure

@@ -513,13 +513,13 @@ disable_weak(){
 
 enable_sanitized(){
     for var; do
-        enable $(echo "$var" | sed 's/[^A-Za-z0-9_]/_/g')
+        enable $(sanitize_var_name $var)
     done
 }
 
 disable_sanitized(){
     for var; do
-        disable $(echo "$var" | sed 's/[^A-Za-z0-9_]/_/g')
+        disable $(sanitize_var_name $var)
     done
 }
 
@@ -552,12 +552,12 @@ enable_deep_weak(){
 }
 
 enabled(){
-    test "${1#!}" = "$1" && op== || op=!=
+    test "${1#!}" = "$1" && op="=" || op="!="
     eval test "x\$${1#!}" $op "xyes"
 }
 
 disabled(){
-    test "${1#!}" = "$1" && op== || op=!=
+    test "${1#!}" = "$1" && op="=" || op="!="
     eval test "x\$${1#!}" $op "xno"
 }
 
@@ -899,6 +899,7 @@ check_objcflags(){
 
 test_ldflags(){
     log test_ldflags "$@"
+    set -- $($ldflags_filter "$@")
     check_ld "$@" <<EOF
 int main(void){ return 0; }
 EOF
@@ -1125,14 +1126,14 @@ require(){
 }
 
 require_header(){
-    log require "$@"
+    log require_header "$@"
     headers="$1"
     shift
     check_header "$headers" "$@" || die "ERROR: $headers not found"
 }
 
 require_cpp_condition(){
-    log require "$@"
+    log require_cpp_condition "$@"
     header="$1"
     condition="$2"
     shift 2