libraries/rapidjson: Fix build with gcc7

I ran into this trying to build rapidjson on ARM -current:
https://github.com/Tencent/rapidjson/pull/941

Signed-off-by: Robby Workman <rworkman@slackbuilds.org>

libraries/rapidjson/fix-build-on-gcc7.diff

@@ -0,0 +1,13 @@
+diff -Nur rapidjson-1.1.0.orig/include/rapidjson/internal/regex.h rapidjson-1.1.0/include/rapidjson/internal/regex.h
+--- rapidjson-1.1.0.orig/include/rapidjson/internal/regex.h	2016-08-25 02:59:05.000000000 -0500
++++ rapidjson-1.1.0/include/rapidjson/internal/regex.h	2017-12-27 01:10:17.765316098 -0600
+@@ -29,6 +29,9 @@
+ #ifdef __GNUC__
+ RAPIDJSON_DIAG_PUSH
+ RAPIDJSON_DIAG_OFF(effc++)
++#if __GNUC__ >= 7
++RAPIDJSON_DIAG_OFF(implicit-fallthrough)
++#endif
+ #endif
+ 
+ #ifdef _MSC_VER

libraries/rapidjson/rapidjson.SlackBuild

@@ -24,7 +24,7 @@
 
 PRGNAM=rapidjson
 VERSION=${VERSION:-1.1.0}
-BUILD=${BUILD:-1}
+BUILD=${BUILD:-2}
 TAG=${TAG:-_SBo}
 
 if [ -z "$ARCH" ]; then
@@ -69,6 +69,9 @@ find -L . \
  \( -perm 666 -o -perm 664 -o -perm 640 -o -perm 600 -o -perm 444 \
   -o -perm 440 -o -perm 400 \) -exec chmod 644 {} \;
 
+# Patch for -current but should be harmless on -stable
+patch -p1 < $CWD/fix-build-on-gcc7.diff
+
 mkdir -p build
 cd build
   cmake \