[OpenMP] Use more compatible flags format

[mati865]

Summary

MSYS2 threats strings starting with forward slashes as paths (similarly to UNIX). We have been replacing them with - using sed but I think it'd be beneficial to solve it upstream.
I cannot test MSVC but AFAIK it accepts both formats.

openmp/runtime/cmake/LibompHandleFlags.cmake

 function(libomp_get_asmflags asmflags)
   set(asmflags_local)
   libomp_append(asmflags_local "-x assembler-with-cpp" LIBOMP_HAVE_X_ASSEMBLER_WITH_CPP_FLAG)
   # Architectural assembler flags
   if(${IA32})
     if(CMAKE_SIZEOF_VOID_P EQUAL 8)
       libomp_append(asmflags_local -m32 LIBOMP_HAVE_M32_FLAG)
     endif()
-    libomp_append(asmflags_local /safeseh LIBOMP_HAVE_SAFESEH_MASM_FLAG)
-    libomp_append(asmflags_local /coff LIBOMP_HAVE_COFF_MASM_FLAG)
+    libomp_append(asmflags_local -safeseh LIBOMP_HAVE_SAFESEH_MASM_FLAG)
+    libomp_append(asmflags_local -coff LIBOMP_HAVE_COFF_MASM_FLAG)
   elseif(${MIC})
     libomp_append(asmflags_local -mmic LIBOMP_HAVE_MMIC_FLAG)
   endif()
   set(asmflags_local ${asmflags_local} ${LIBOMP_ASMFLAGS})
   libomp_setup_flags(asmflags_local)
   set(${asmflags} ${asmflags_local} PARENT_SCOPE)
 endfunction()
 
 # Linker flags
 function(libomp_get_ldflags ldflags)
   set(ldflags_local)
   libomp_append(ldflags_local "${CMAKE_LINK_DEF_FILE_FLAG}${CMAKE_CURRENT_BINARY_DIR}/${LIBOMP_LIB_NAME}.def"
     IF_DEFINED CMAKE_LINK_DEF_FILE_FLAG)
   libomp_append(ldflags_local "${CMAKE_C_OSX_CURRENT_VERSION_FLAG}${LIBOMP_VERSION_MAJOR}.${LIBOMP_VERSION_MINOR}"
     IF_DEFINED CMAKE_C_OSX_CURRENT_VERSION_FLAG)
   libomp_append(ldflags_local "${CMAKE_C_OSX_COMPATIBILITY_VERSION_FLAG}${LIBOMP_VERSION_MAJOR}.${LIBOMP_VERSION_MINOR}"
     IF_DEFINED CMAKE_C_OSX_COMPATIBILITY_VERSION_FLAG)
   libomp_append(ldflags_local -Wl,--warn-shared-textrel LIBOMP_HAVE_WARN_SHARED_TEXTREL_FLAG)
   libomp_append(ldflags_local -Wl,--as-needed LIBOMP_HAVE_AS_NEEDED_FLAG)
   libomp_append(ldflags_local "-Wl,--version-script=${LIBOMP_SRC_DIR}/exports_so.txt" LIBOMP_HAVE_VERSION_SCRIPT_FLAG)
   libomp_append(ldflags_local -static-libgcc LIBOMP_HAVE_STATIC_LIBGCC_FLAG)
   libomp_append(ldflags_local -Wl,-z,noexecstack LIBOMP_HAVE_Z_NOEXECSTACK_FLAG)
   libomp_append(ldflags_local -no-intel-extensions LIBOMP_HAVE_NO_INTEL_EXTENSIONS_FLAG)
   libomp_append(ldflags_local -static-intel LIBOMP_HAVE_STATIC_INTEL_FLAG)
-  libomp_append(ldflags_local /SAFESEH LIBOMP_HAVE_SAFESEH_FLAG)
+  libomp_append(ldflags_local -SAFESEH LIBOMP_HAVE_SAFESEH_FLAG)
   # Architectural linker flags
   if(${IA32})
     if(CMAKE_SIZEOF_VOID_P EQUAL 8)
       libomp_append(ldflags_local -m32 LIBOMP_HAVE_M32_FLAG)
     endif()
     libomp_append(ldflags_local -msse2 LIBOMP_HAVE_MSSE2_FLAG)
   elseif(${MIC})
     libomp_append(ldflags_local -mmic LIBOMP_HAVE_MMIC_FLAG)

openmp/runtime/cmake/LibompMicroTests.cmake

if(LIBOMP_SHELL)
     set(libomp_test_touch_targets test-touch-md/.success test-touch-mt/.success)
   endif()
   # pick test-touch compiler
   set(libomp_test_touch_compiler ${CMAKE_C_COMPILER})
   # test-touch compilation flags
   libomp_append(libomp_test_touch_cflags /nologo)
   libomp_append(libomp_test_touch_libs ${LIBOMPIMP_OUTPUT_DIRECTORY}/${LIBOMP_IMP_LIB_FILE})
   if(${IA32})
-    libomp_append(libomp_test_touch_ldflags /safeseh)
+    libomp_append(libomp_test_touch_ldflags -safeseh)
   endif()
 else() # (Unix based systems, Intel(R) MIC Architecture, and Mac)
   if(LIBOMP_SHELL)
     set(libomp_test_touch_targets test-touch-rt/.success)
   endif()
   # pick test-touch compiler
   if(${LIBOMP_USE_STDCPPLIB})
     set(libomp_test_touch_compiler ${CMAKE_CXX_COMPILER})

openmp/runtime/cmake/config-ix.cmake

 if (NOT LIBOMP_HAVE_SHM_OPEN_NO_LRT)
   set(CMAKE_REQUIRED_LIBRARIES -lrt)
   check_symbol_exists(shm_open "sys/mman.h" LIBOMP_HAVE_SHM_OPEN_WITH_LRT)
   set(CMAKE_REQUIRED_LIBRARIES)
 endif()
 
 # Check linker flags
 if(WIN32)
-  libomp_check_linker_flag(/SAFESEH LIBOMP_HAVE_SAFESEH_FLAG)
+  libomp_check_linker_flag(-SAFESEH LIBOMP_HAVE_SAFESEH_FLAG)
 elseif(NOT APPLE)
   libomp_check_linker_flag(-Wl,-x LIBOMP_HAVE_X_FLAG)
   libomp_check_linker_flag(-Wl,--warn-shared-textrel LIBOMP_HAVE_WARN_SHARED_TEXTREL_FLAG)
   libomp_check_linker_flag(-Wl,--as-needed LIBOMP_HAVE_AS_NEEDED_FLAG)
   libomp_check_linker_flag("-Wl,--version-script=${LIBOMP_SRC_DIR}/exports_so.txt" LIBOMP_HAVE_VERSION_SCRIPT_FLAG)
   libomp_check_linker_flag(-static-libgcc LIBOMP_HAVE_STATIC_LIBGCC_FLAG)
   libomp_check_linker_flag(-Wl,-z,noexecstack LIBOMP_HAVE_Z_NOEXECSTACK_FLAG)
 endif()