[PATCH dwarves v2] Respect CMAKE_INSTALL_LIBDIR

[Ben Olson <matthew.olson@intel.com>]

This patch changes the `cmake` configuration to honor `CMAKE_INSTALL_LIBDIR`
and use either `lib` or `lib64` by default so that installations match the
conventional placement of libraries.
For example, it will now install `libdwarves.so` into `${PREFIX}/lib` or
`${PREFIX}/lib64`, depending on the distribution.

Signed-off-by: Brandon Kammerdiener <brandon.kammerdiener@intel.com>
Signed-off-by: Ben Olson <matthew.olson@intel.com>
Cc: Alan Maguire <alan.maguire@oracle.com>
---

Changes in v2:
  - Included the proper built-in CMake module
  - Made commit message distro-agnostic

 CMakeLists.txt | 19 ++++++-------------
 README         |  3 +--
 2 files changed, 7 insertions(+), 15 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8ca1bf2..1d0dadf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,18 +21,9 @@ else()
 	LINK_DIRECTORIES(${LIBBPF_LIBRARY_DIRS})
 endif()
 
-# Try to parse this later, Helio just showed me a KDE4 example to support
-# x86-64 builds.
-# the following are directories where stuff will be installed to
-set(__LIB "" CACHE STRING "Define suffix of directory name (32/64)" )
-
-macro(_set_fancy _var _value _comment)
-	if (NOT DEFINED ${_var})
-		set(${_var} ${_value})
-	else (NOT DEFINED ${_var})
-		set(${_var} "${${_var}}" CACHE PATH "${_comment}")
-	endif (NOT DEFINED ${_var})
-endmacro(_set_fancy)
+# Use the standard library installation directory
+include(GNUInstallDirs)
+set(CMAKE_INSTALL_LIBDIR "lib" CACHE STRING "libdir name")
 
 # where to look first for cmake modules,
 # before ${CMAKE_ROOT}/Modules/ is checked
@@ -84,7 +75,9 @@ if(NOT LIBBPF_FOUND AND NOT EXISTS "${PROJECT_SOURCE_DIR}/lib/bpf/src/btf.h")
 	message(FATAL_ERROR "The submodules were not downloaded! GIT_SUBMODULE was turned off or failed. Please update submodules and try again.")
 endif()
 
-_set_fancy(LIB_INSTALL_DIR "${EXEC_INSTALL_PREFIX}${CMAKE_INSTALL_PREFIX}/${__LIB}" "libdir")
+if (NOT DEFINED LIB_INSTALL_DIR)
+    set(LIB_INSTALL_DIR "${EXEC_INSTALL_PREFIX}${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}")
+endif()
 
 # libbpf uses reallocarray, which is not available in all versions of glibc
 # libbpf's include/tools/libc_compat.h provides implementation, but needs
diff --git a/README b/README
index f9aeef7..0627872 100644
--- a/README
+++ b/README
@@ -3,8 +3,7 @@ Build instructions:
 1. install cmake
 2. mkdir build
 3. cd build
-4. cmake -D__LIB=lib ..
-5. make install
+4. make install
 
 cmake Options:
   -DBUILD_SHARED_LIBS
-- 
2.47.0