curl-compilers.m4: -Wno-pedantic-ms-format for Windows gcc 4.5 builds

When building a Windows target with gcc 4.5 or newer and strict compiler
warnings enabled use -Wno-pedantic-ms-format in addition to other flags.

m4/curl-compilers.m4

@@ -21,7 +21,7 @@
 #***************************************************************************
 
 # File version for 'aclocal' use. Keep it a single number.
-# serial 60
+# serial 61
 
 
 dnl CURL_CHECK_COMPILER
@@ -161,6 +161,7 @@ AC_DEFUN([CURL_CHECK_COMPILER_GNU_C], [
     flags_opt_all="-O -O0 -O1 -O2 -O3 -Os"
     flags_opt_yes="-O2"
     flags_opt_off="-O0"
+    CURL_CHECK_DEF([_WIN32], [], [silent])
   else
     AC_MSG_RESULT([no])
   fi
@@ -977,6 +978,14 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
             tmp_CFLAGS="$tmp_CFLAGS -Wconversion -Wno-sign-conversion -Wvla"
           fi
           #
+          dnl Only gcc 4.5 or later
+          if test "$compiler_num" -ge "405"; then
+            dnl Only windows targets
+            if test "$curl_cv_have_def__WIN32" = "yes"; then
+              tmp_CFLAGS="$tmp_CFLAGS -Wno-pedantic-ms-format"
+            fi
+          fi
+          #
         fi
         #
         dnl Do not issue warnings for code in system include paths.