Ports: Add flatbuffers library (#6050)

The flatbuffers library is a serialization library, created by Google
for game development and performance-critical applications.
It aims to be fast and efficient.

This commit creates a port of it to SerenityOS.

The flatbuffers build process generates three things: some header files,
a library (libflatbuffers) and a schema compiler (flatc).

There are tests, but they are not compiled, because it runs the
flatbuffers schema compiler, one of the things we are cross-compiling.
The compiler will not run because the target is different from the host

Ports/AvailablePorts.md

@@ -23,6 +23,7 @@ Please make sure to keep this list up to date when adding and updating ports. :^
 | [`dropbear`](dropbear/)        | Dropbear SSH                                  | 2019.78           | https://dropbear.nl/mirror/dropbear.html              |
 | [`ed`](ed/)                    | GNU ed                                        | 1.15              | https://www.gnu.org/software/ed/                      |
 | [`figlet`](figlet/)            | FIGlet                                        | 2.2.5             | http://www.figlet.org/                                |
+| [`flatbuffers`](flatbuffers/)  | Flatbuffers                                   | 1.12.0            | https://github.com/google/flatbuffers                 |
 | [`flex`](flex/)                | flex                                          | 2.6.4             | https://github.com/westes/flex                        |
 | [`freetype`](freetype/)        | FreeType                                      | 2.10.4            | https://www.freetype.org/                             |
 | [`frotz`](frotz/)              | Frotz                                         |                   | https://gitlab.com/DavidGriffith/frotz                |

Ports/flatbuffers/package.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+
+port="flatbuffers"
+version="1.12.0"
+auth_type=sha256
+files="https://github.com/google/flatbuffers/archive/refs/tags/v${version}.tar.gz v${version}.tar.gz 62f2223fb9181d1d6338451375628975775f7522185266cd5296571ac152bc45"
+useconfigure=true
+# Since we are cross-compiling, we cannot build the tests, because we need
+# the flatbuffers compiler to build them
+configopts="-DCMAKE_TOOLCHAIN_FILE=$SERENITY_ROOT/Toolchain/CMakeToolchain.txt -DFLATBUFFERS_BUILD_TESTS=off"
+
+configure() {
+    run cmake $configopts
+}
+
+install() {
+    run make install
+}

Ports/flatbuffers/patches/flatbuffers-1.12.0.patch

@@ -0,0 +1,21 @@
+diff -ruN flatbuffers-1.12.0/src/code_generators.cpp flatbuffers-1.12.0-serenity/src/code_generators.cpp
+--- flatbuffers-1.12.0/src/code_generators.cpp	2020-03-12 19:33:39.000000000 -0300
++++ flatbuffers-1.12.0-serenity/src/code_generators.cpp	2021-03-31 20:39:12.000000000 -0300
+@@ -23,6 +23,17 @@
+ #include "flatbuffers/base.h"
+ #include "flatbuffers/util.h"
+ 
++#if defined(__serenity__)
++  // We do not have those functions inside std namespace...
++
++namespace std {
++  auto isnan(double x) { return ::isnan(x); }
++  auto isinf(double x) { return ::isinf(x); }
++}
++
++#endif
++
++
+ #if defined(_MSC_VER)
+ #  pragma warning(push)
+ #  pragma warning(disable : 4127)  // C4127: conditional expression is constant