Teach find_(library|package) about Linux multiarch (#12037)

Implement support for multiarch as specified here:

  http://wiki.debian.org/Multiarch
  https://wiki.ubuntu.com/MultiarchSpec

Detect the <arch> part of <prefix>/lib/<arch> from the implicit library
search path from each compiler to set CMAKE_<lang>_LIBRARY_ARCHITECTURE.
Define CMAKE_LIBRARY_ARCHITECTURE using one of these values (they should
all be the same).  Teach the find_library and find_package commands to
search <prefix>/lib/<arch> whenever they would search <prefix>/lib.

1 files changed, 20 insertions, 0 deletions

diff --git a/Source/cmDocumentVariables.cxx b/Source/cmDocumentVariables.cxx
index 994445d..ea25e60 100644
--- a/Source/cmDocumentVariables.cxx
+++ b/Source/cmDocumentVariables.cxx
@@ -822,6 +822,18 @@ void cmDocumentVariables::DefineVariables(cmake* cm)
      "set to the output of uname -r. On other "
      "systems this is set to major-minor version numbers.",false,
      "Variables That Describe the System");
+  cm->DefineProperty
+    ("CMAKE_LIBRARY_ARCHITECTURE", cmProperty::VARIABLE,
+     "Target architecture library directory name, if detected.",
+     "This is the value of CMAKE_<lang>_LIBRARY_ARCHITECTURE as "
+     "detected for one of the enabled languages.",false,
+     "Variables That Describe the System");
+  cm->DefineProperty
+    ("CMAKE_LIBRARY_ARCHITECTURE_REGEX", cmProperty::VARIABLE,
+     "Regex matching possible target architecture library directory names.",
+     "This is used to detect CMAKE_<lang>_LIBRARY_ARCHITECTURE from the "
+     "implicit linker search path by matching the <arch> name.",false,
+     "Variables That Describe the System");
 
   cm->DefineProperty
     ("CMAKE_HOST_SYSTEM", cmProperty::VARIABLE,
@@ -1360,6 +1372,14 @@ void cmDocumentVariables::DefineVariables(cmake* cm)
      "Variables for Languages");
 
   cm->DefineProperty
+    ("CMAKE_<LANG>_LIBRARY_ARCHITECTURE", cmProperty::VARIABLE,
+     "Target architecture library directory name detected for <lang>.",
+     "If the <lang> compiler passes to the linker an architecture-specific "
+     "system library search directory such as <prefix>/lib/<arch> this "
+     "variable contains the <arch> name if/as detected by CMake.",false,
+     "Variables for Languages");
+
+  cm->DefineProperty
     ("CMAKE_<LANG>_LINKER_PREFERENCE_PROPAGATES", cmProperty::VARIABLE,
      "True if CMAKE_<LANG>_LINKER_PREFERENCE propagates across targets.",
      "This is used when CMake selects a linker language for a target.  "