json-c++: add pkg-config patch.

This patch already exists upstream, but is needed for nwg-launchers.

srcpkgs/json-c++/patches/pkg-config.patch

@@ -0,0 +1,59 @@
+From c7d18c16259048878ab566c30aea2078a94b58fe Mon Sep 17 00:00:00 2001
+From: Palmer Dabbelt <palmer@dabbelt.com>
+Date: Thu, 8 Aug 2019 14:36:27 -0700
+Subject: [PATCH] cmake: Generate and install a pkg-config file.
+
+The meson builds install a pkg-config file, but the cmake builds don't.
+This adds a pkg-config file to the cmake builds that is functionally
+equivalent to the one generated from meson.
+---
+ CMakeLists.txt         | 12 +++++++++++-
+ cmake/pkg-config.pc.in |  4 ++++
+ 2 files changed, 15 insertions(+), 1 deletion(-)
+ create mode 100644 cmake/pkg-config.pc.in
+
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index f7ba4fa38..372a7a03a 100644
+--- CMakeLists.txt
++++ CMakeLists.txt
+@@ -4,7 +4,7 @@ cmake_minimum_required(VERSION 3.1)
+ ## PROJECT
+ ## name and version
+ ##
+-project(nlohmann_json VERSION 3.8.0 LANGUAGES CXX)
++project(nlohmann_json VERSION 3.8.0 DESCRIPTION "JSON for Modern C++" LANGUAGES CXX)
+ 
+ ##
+ ## INCLUDE
+@@ -79,6 +79,12 @@ if (MSVC)
+     )
+ endif()
+ 
++# Install a pkg-config file, so other tools can find this.
++CONFIGURE_FILE(
++  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/pkg-config.pc.in"
++  "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
++)
++
+ ##
+ ## TESTS
+ ## create and configure the unit test target
+@@ -139,4 +145,8 @@ endif()
+         NAMESPACE ${PROJECT_NAME}::
+         DESTINATION ${NLOHMANN_JSON_CONFIG_INSTALL_DIR}
+     )
++    install(
++        FILES "${CMAKE_BINARY_DIR}/${PROJECT_NAME}.pc"
++        DESTINATION lib/pkgconfig
++    )
+ endif()
+diff --git a/cmake/pkg-config.pc.in b/cmake/pkg-config.pc.in
+new file mode 100644
+index 000000000..680f10c26
+--- /dev/null
++++ cmake/pkg-config.pc.in
+@@ -0,0 +1,4 @@
++Name: ${PROJECT_NAME}
++Description: ${PROJECT_DESCRIPTION}
++Version: ${PROJECT_VERSION}
++Cflags: -I${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_INCLUDEDIR}

srcpkgs/json-c++/template

@@ -1,7 +1,7 @@
 # Template file for 'json-c++'
 pkgname=json-c++
 version=3.8.0
-revision=1
+revision=2
 wrksrc="json-${version}"
 build_style=cmake
 short_desc="JSON for modern C++"