In pkg-config File, Derive Lib and Include Dir from Prefix at Use-Time

Addresses #1794. Instead of deriving the lib dir and include dir at
build-time, let's do it like everyone else does at pkg-config run-time.

This has the disadvantage that we can no longer override LIBDIR and
INCLUDEDIR in the Makefile and have that reflected in the .pc file.

build/cmake/lib/CMakeLists.txt

@@ -134,11 +134,10 @@ if (UNIX)
     # pkg-config
     set(PREFIX "${CMAKE_INSTALL_PREFIX}")
     set(LIBDIR "${CMAKE_INSTALL_FULL_LIBDIR}")
-    set(INCLUDEDIR "${CMAKE_INSTALL_FULL_INCLUDEDIR}")
     set(VERSION "${zstd_VERSION_MAJOR}.${zstd_VERSION_MINOR}.${zstd_VERSION_PATCH}")
     add_custom_target(libzstd.pc ALL
             ${CMAKE_COMMAND} -DIN="${LIBRARY_DIR}/libzstd.pc.in" -DOUT="libzstd.pc"
-            -DPREFIX="${PREFIX}" -DLIBDIR="${LIBDIR}" -DINCLUDEDIR="${INCLUDEDIR}" -DVERSION="${VERSION}"
+            -DPREFIX="${PREFIX}" -DVERSION="${VERSION}"
             -P "${CMAKE_CURRENT_SOURCE_DIR}/pkgconfig.cmake"
             COMMENT "Creating pkg-config file")
 

lib/Makefile

@@ -244,8 +244,6 @@ libzstd.pc:
 libzstd.pc: libzstd.pc.in
 	@echo creating pkgconfig
 	@sed -e 's|@PREFIX@|$(PREFIX)|' \
-             -e 's|@LIBDIR@|$(LIBDIR)|' \
-             -e 's|@INCLUDEDIR@|$(INCLUDEDIR)|' \
              -e 's|@VERSION@|$(VERSION)|' \
              $< >$@
 

lib/libzstd.pc.in

@@ -3,8 +3,9 @@
 #   BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
 
 prefix=@PREFIX@
-libdir=@LIBDIR@
-includedir=@INCLUDEDIR@
+exec_prefix=${prefix}
+includedir=${prefix}/include
+libdir=${exec_prefix}/lib
 
 Name: zstd
 Description: fast lossless compression algorithm library