Add the project option LAPACK_BINARY_PATH_SUFFIX

It names a subdirectory added to the install location of all LAPACK
binaries. It is empty by default.

This allows a consumer, to install the Reference LAPACK binaries into a
subdirectory of, e.g., `/usr/local/lib` without inadvertantly changing
the install location of the CMake package scripts, which remain
unchanged in `/usr/local/lib/cmake`.

This can be necessary to avoid conflicts with other BLAS/LAPACK
distributions. Previously, this would require the consumer to override
`CMAKE_INSTALL_LIBDIR` directly. This shouldn't be done, though, because
the variable is provided by the core CMake module GNUInstallDirs and is
used in many places. Thus, changing it can have unforeseen consequences.
Here, overriding it also changed the install locations of the CMake
package scripts and PKGConfig files, which prevents them from being
discovered by default by their respective tools.

Author: lepus2589

CMakeLists.txt

@@ -159,12 +159,18 @@ endif()
 # --------------------------------------------------
 set(LAPACK_INSTALL_EXPORT_NAME ${LAPACKLIB}-targets)
 
+set(LAPACK_BINARY_PATH_SUFFIX "" CACHE STRING "Path suffix appended to the install path of binaries")
+
+if(NOT "${LAPACK_BINARY_PATH_SUFFIX}" STREQUAL "" AND NOT "${LAPACK_BINARY_PATH_SUFFIX}" MATCHES "^/")
+  set(LAPACK_BINARY_PATH_SUFFIX "/${LAPACK_BINARY_PATH_SUFFIX}")
+endif()
+
 macro(lapack_install_library lib)
   install(TARGETS ${lib}
     EXPORT ${LAPACK_INSTALL_EXPORT_NAME}
-    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT Development
-    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT RuntimeLibraries
-    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR} COMPONENT RuntimeLibraries
+    ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}${LAPACK_BINARY_PATH_SUFFIX}" COMPONENT Development
+    LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}${LAPACK_BINARY_PATH_SUFFIX}" COMPONENT RuntimeLibraries
+    RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}${LAPACK_BINARY_PATH_SUFFIX}" COMPONENT RuntimeLibraries
   )
 endmacro()
 
@@ -557,7 +563,7 @@ install(FILES
 if (LAPACK++)
   install(
   DIRECTORY "${LAPACK_BINARY_DIR}/lib/"
-  DESTINATION ${CMAKE_INSTALL_LIBDIR}
+  DESTINATION "${CMAKE_INSTALL_LIBDIR}${LAPACK_BINARY_PATH_SUFFIX}"
   FILES_MATCHING REGEX "liblapackpp.(a|so)$"
   )
   install(
@@ -590,7 +596,7 @@ if (BLAS++)
   )
   install(
   DIRECTORY "${LAPACK_BINARY_DIR}/lib/"
-  DESTINATION ${CMAKE_INSTALL_LIBDIR}
+  DESTINATION "${CMAKE_INSTALL_LIBDIR}${LAPACK_BINARY_PATH_SUFFIX}"
   FILES_MATCHING REGEX "libblaspp.(a|so)$"
   )
   install(