jsoncpp: Fix pkgconfig file

Backported upstream patch to make the pkgconfig file more cross compile
friendly. I don't think anything uses this.

Replaced Installev with CMAKE_INSTALL.

Added PKG_BUILD_PARALLEL for faster compilation.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/jsoncpp/patches/010-pkgconnfig.patch

@@ -0,0 +1,26 @@
+From 63dc2f77e33e9ff559e051cd2964960b9d3e761e Mon Sep 17 00:00:00 2001
+From: Rosen Penev <rosenp@gmail.com>
+Date: Mon, 16 Sep 2019 18:38:24 -0700
+Subject: [PATCH] pkgconfig: Fix for cross compilation
+
+exec_ and prefix must be overridden  in such a case.
+
+Makes the .pc file more consistent with other projects.
+---
+ pkg-config/jsoncpp.pc.in | 6 ++++--
+ 1 file changed, 4 insertions(+), 2 deletions(-)
+
+diff --git a/pkg-config/jsoncpp.pc.in b/pkg-config/jsoncpp.pc.in
+index dea51f51..d4fa9ef2 100644
+--- a/pkg-config/jsoncpp.pc.in
++++ b/pkg-config/jsoncpp.pc.in
+@@ -1,5 +1,7 @@
+-libdir=@CMAKE_INSTALL_FULL_LIBDIR@
+-includedir=@CMAKE_INSTALL_FULL_INCLUDEDIR@
++prefix=@CMAKE_INSTALL_PREFIX@
++exec_prefix=@CMAKE_INSTALL_PREFIX@
++libdir=${exec_prefix}/@CMAKE_INSTALL_LIBDIR@
++includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+ 
+ Name: jsoncpp
+ Description: A C++ library for interacting with JSON