Fix pkg-config file generation, backported from upstream commit:
https://github.com/coin-or/CppAD/commit/6d10b8d
with an additional fix to not have -l-lcppad_lib
--- a/pkgconfig/CMakeLists.txt
+++ b/pkgconfig/CMakeLists.txt
@@ -124,3 +124,3 @@
 # cppad_includedir
-LIST(GET cmake_install_libdirs 0 cppad_includedir)
+LIST(GET cmake_install_includedirs 0 cppad_includedir)
 #
@@ -161,2 +161,3 @@
     ${CMAKE_CURRENT_BINARY_DIR}/cppad.pc
+    @ONLY
 )
--- a/pkgconfig/cppad.pc.in
+++ b/pkgconfig/cppad.pc.in
@@ -17,3 +17,3 @@
 prefix=@cppad_prefix@
-exec_prefix=$(prefix)
+exec_prefix=${prefix}
 includedir=${prefix}/@cppad_includedir@
@@ -30,3 +30,3 @@
 Cflags:                -I${includedir}
-Libs:                  -L{libdir} -l@cppad_lib_list@
+Libs:                  -L${libdir} @cppad_lib_list@
 Requires: