FindPkgConfig: Fix parsing of backslash-escaped spaces in pkg-config output

Treat backslash-escaped spaces as "space within argument" rather than
"space delimiting arguments".

Update our `FindPkgConfig_LIBRARY_PATH` test case to escape spaces in
the path, and run it unconditionally.

Modules/FindPkgConfig.cmake

@@ -143,7 +143,9 @@ macro(_pkgconfig_invoke _pkglist _prefix _varname _regexp)
       string(REGEX REPLACE "${_regexp}" " " _pkgconfig_invoke_result "${_pkgconfig_invoke_result}")
     endif()
 
-    separate_arguments(_pkgconfig_invoke_result)
+    # pkg-config can represent "spaces within an argument" by backslash-escaping the space.
+    # UNIX_COMMAND mode treats backslash-escaped spaces as "not a space that delimits arguments".
+    separate_arguments(_pkgconfig_invoke_result UNIX_COMMAND "${_pkgconfig_invoke_result}")
 
     #message(STATUS "  ${_varname} ... ${_pkgconfig_invoke_result}")
     set(_pkgconfig_${_varname} ${_pkgconfig_invoke_result})

Tests/RunCMake/FindPkgConfig/FindPkgConfig_LIBRARY_PATH-stdout.txt

@@ -1,3 +1,3 @@
 -- ZOT_LIBRARIES='zot'
--- ZOT_LINK_LIBRARIES='[^']*/Tests/RunCMake/FindPkgConfig/FindPkgConfig_LIBRARY_PATH-build/zot/lib/prefix-zot-suffix'
--- ZOT_LDFLAGS='-L[^']*/Tests/RunCMake/FindPkgConfig/FindPkgConfig_LIBRARY_PATH-build/zot/lib;-lzot'
+-- ZOT_LINK_LIBRARIES='[^']*/Tests/RunCMake/FindPkgConfig/FindPkgConfig_LIBRARY_PATH-build/root/lib/prefix-zot-suffix'
+-- ZOT_LDFLAGS='-L[^']*/Tests/RunCMake/FindPkgConfig/FindPkgConfig_LIBRARY_PATH-build/root/lib;-lzot'

Tests/RunCMake/FindPkgConfig/FindPkgConfig_LIBRARY_PATH.cmake

@@ -1,11 +1,16 @@
 find_package(PkgConfig REQUIRED)
 
-file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/zot/lib/pkgconfig/zot.pc" "
-prefix=${CMAKE_CURRENT_BINARY_DIR}/zot
+set(ROOT "${CMAKE_CURRENT_BINARY_DIR}/root")
+string(REPLACE " " "\\ " ESCAPED_ROOT "${ROOT}")
+set(LIB_DIR "${ROOT}/lib")
+set(PKGCONFIG_DIR "${LIB_DIR}/pkgconfig")
+
+file(WRITE "${PKGCONFIG_DIR}/zot.pc" "
+prefix=${ESCAPED_ROOT}
 libdir=\${prefix}/lib
 
 Name: Zot
-Description: Dummy packaget to test LIBRARY_DIR support
+Description: Dummy package to test LIBRARY_DIR support
 Version: 1.0
 Libs: -L\${libdir} -lzot
 ")
@@ -13,15 +18,15 @@ Libs: -L\${libdir} -lzot
 # Create a "library" file to find in libdir.
 set(CMAKE_FIND_LIBRARY_PREFIXES "prefix-")
 set(CMAKE_FIND_LIBRARY_SUFFIXES "-suffix")
-file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/zot/lib/prefix-zot-suffix")
+file(WRITE "${LIB_DIR}/prefix-zot-suffix")
 
 # 'pkg-config --libs' drops -L flags in PKG_CONFIG_SYSTEM_LIBRARY_PATH by default.
-set(ENV{PKG_CONFIG_SYSTEM_LIBRARY_PATH} "${CMAKE_CURRENT_BINARY_DIR}/zot/lib")
+set(ENV{PKG_CONFIG_SYSTEM_LIBRARY_PATH} "${LIB_DIR}")
 
 # 'pkgconf --libs' also drops -L flags in LIBRARY_PATH by default.
-set(ENV{LIBRARY_PATH}                   "${CMAKE_CURRENT_BINARY_DIR}/zot/lib")
+set(ENV{LIBRARY_PATH}                   "${LIB_DIR}")
 
-set(ENV{PKG_CONFIG_PATH}                "${CMAKE_CURRENT_BINARY_DIR}/zot/lib/pkgconfig")
+set(ENV{PKG_CONFIG_PATH}                "${PKGCONFIG_DIR}")
 pkg_check_modules(ZOT REQUIRED zot)
 
 message(STATUS "ZOT_LIBRARIES='${ZOT_LIBRARIES}'")

Tests/RunCMake/FindPkgConfig/RunCMakeTest.cmake

@@ -32,8 +32,5 @@ if (PKG_CONFIG_FOUND)
   run_cmake(FindPkgConfig_VERSION_OPERATORS)
   run_cmake(FindPkgConfig_GET_MATCHING_MODULE_NAME)
   run_cmake(FindPkgConfig_empty_target)
-
-  if(NOT RunCMake_BINARY_DIR MATCHES " ")
-    run_cmake(FindPkgConfig_LIBRARY_PATH)
-  endif()
+  run_cmake(FindPkgConfig_LIBRARY_PATH)
 endif ()