Detect if libomp is supported in the environment

From LLVM 18, libomp is supported in s390x. Previously all the libomp related
tests were marked as XFAIL for s390x, which is no longer valid and marks
passing tests as failures. With the libomp detection and a new REQUIRE rule for
them the XFAIL is no longer needed.

CMakeLists.txt

@@ -63,6 +63,25 @@ option(ENABLE_HWASAN
     ${SUPPORT_HWASAN}
     )
 
+# Detect if libomp is supported in the current host. Setting it manually in all
+# the environments can be tricky as s390x supports it only in llvm < 18
+# This can still be explicitly enforced via -DENABLE_LIBOMP=ON|OFF
+file(WRITE ${CMAKE_BINARY_DIR}/test.c "int main(){return 0;}")
+message(STATUS "Checking libomp support")
+execute_process(COMMAND
+    ${CLANG_BINARY} -x c -fopenmp ${CMAKE_BINARY_DIR}/test.c
+    RESULT_VARIABLE PROC_RETURN
+    )
+if (PROC_RETURN EQUAL 0)
+    set(SUPPORT_LIBOMP ON)
+else()
+    message(STATUS "libomp not supported, related tests will be disabled")
+    set(SUPPORT_LIBOMP OFF)
+endif()
+OPTION(ENABLE_LIBOMP
+    "Enable tests that require libomp"
+    ${SUPPORT_LIBOMP})
+
 configure_file(
     ${CMAKE_CURRENT_SOURCE_DIR}/tests/lit.site.cfg.in
     ${CMAKE_BINARY_DIR}/tests/lit.site.cfg

tests/basic_openmp.c

@@ -2,8 +2,7 @@
 //
 // RUN: %clang -fopenmp %s -o %t
 // RUN: %t | grep "Num Threads: 1"
-// REQUIRES: clang
-// XFAIL: s390x
+// REQUIRES: clang, libomp
 
 #include <omp.h>
 #include <stdio.h>

tests/lit.site.cfg.in

@@ -52,3 +52,4 @@ enable_feature("libc++", "@ENABLE_LIBCXX@")
 enable_feature("static-libc++", "@ENABLE_STATIC_LIBCXX@")
 enable_feature("libunwind", "@ENABLE_LIBUNWIND@")
 enable_feature("support_hwasan", "@ENABLE_HWASAN@")
+enable_feature("libomp", "@ENABLE_LIBOMP@")

tests/openmp_headers.c

@@ -1,8 +1,7 @@
 // Test OpenMP headers install
 //
 // RUN: %clang -fopenmp -E %s -o %t
-// REQUIRES: clang
-// XFAIL: s390x
+// REQUIRES: clang, libomp
 
 #include <omp.h>
 #if _OPENMP >= 201811

tests/openmp_tools.c

@@ -2,8 +2,7 @@
 // RUN: %clang -fopenmp -DTOOLS %s -shared -o %t_Tools.so
 // RUN: %clang -fopenmp -UTOOLS %s -o %t
 // RUN: OMP_TOOL_LIBRARIES=%t_Tools.so %t | grep "INIT"
-// REQUIRES: clang
-// XFAIL: s390x
+// REQUIRES: clang, libomp
 #ifdef TOOLS
 
 // OpenMP Tools are only supported starting OpenMP 5