m4/curl-compilers: tell clang -Wno-pointer-bool-conversion

To hush compiler warnings we don't care for: error: address of function
'X' will always evaluate to 'true'

Fixes #8197
Closes #....

m4/curl-compilers.m4

@@ -536,6 +536,9 @@ AC_DEFUN([CURL_SET_COMPILER_BASIC_OPTS], [
         dnl warn about compile-time arguments used during link-time, like
         dnl -O and -g and -pedantic.
         tmp_CFLAGS="$tmp_CFLAGS -Qunused-arguments"
+        dnl Disable pointer to bool conversion warnings since they cause
+        dnl lib/securetransp.c cause several warnings for checks we want.
+        tmp_CFLAGS="$tmp_CFLAGS -Wno-pointer-bool-conversion"
         ;;
         #
       DEC_C)