Tests: Add missing execute_process result checks

Tests/FindPackageModeMakefileTest/CMakeLists.txt

diff --git a/Tests/FindPackageModeMakefileTest/CMakeLists.txt b/Tests/FindPackageModeMakefileTest/CMakeLists.txt
index 0b15be8..a9bcfc4 100644
--- a/Tests/FindPackageModeMakefileTest/CMakeLists.txt
+++ b/Tests/FindPackageModeMakefileTest/CMakeLists.txt
@@ -9,9 +9,10 @@
   execute_process(COMMAND ${CMAKE_MAKE_PROGRAM} -v
                   OUTPUT_VARIABLE makeVersionOutput
                   ERROR_QUIET
-                  TIMEOUT 10)
+                  TIMEOUT 10
+                  RESULT_VARIABLE _make_result)
   string(TOUPPER "${makeVersionOutput}" MAKE_VERSION_OUTPUT)
-  if("${MAKE_VERSION_OUTPUT}" MATCHES "GNU MAKE")
+  if(_make_result EQUAL 0 AND "${MAKE_VERSION_OUTPUT}" MATCHES "GNU MAKE")
 
     # build a library which we can search during the test
     add_library(foo STATIC foo.cpp)

Tests/RunCMake/CMakeLists.txt

diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 6261947..8bf0af3 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -1231,8 +1231,9 @@
   if(UNIX AND NOT CYGWIN)
     execute_process(COMMAND ldd --help
       OUTPUT_VARIABLE LDD_HELP
-      ERROR_VARIABLE LDD_ERR)
-    if("${LDD_HELP}" MATCHES
+      ERROR_VARIABLE LDD_ERR
+      RESULT_VARIABLE LDD_RESULT)
+    if(LDD_RESULT EQUAL 0 AND "${LDD_HELP}" MATCHES
         "(-r, --function-relocs.*process data and function relocations.*-u, --unused.*print unused direct dependencies)")
       add_RunCMake_test(LinkWhatYouUse)
     endif()