[AArch64][FMV] Enable tests for ACLE FMV on Linux.

Enabling Linux part of llvm#87

Author: ilinpv

SingleSource/UnitTests/AArch64/CMakeLists.txt

@@ -1,10 +1,9 @@
 if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
+  if(TARGET_OS STREQUAL "Linux")
+    list(APPEND CFLAGS --rtlib=compiler-rt)
+    list(APPEND LDFLAGS --rtlib=compiler-rt)
+  endif()
   if(ARCH STREQUAL "AArch64")
-    set(Source )
-    # TODO: this test is currently only supported on Darwin platforms:
-    if (TARGET_OS MATCHES "Darwin")
-      list(APPEND Source acle-fmv-features.c)
-    endif()
     llvm_singlesource(PREFIX "aarch64-")
   endif()
 endif()

SingleSource/UnitTests/AArch64/acle-fmv-features.c

@@ -196,7 +196,14 @@ CHECK(ssbs2, {
 CHECK(bti, {
     // The only test for this requires reading a register that is only
     // accessible to EL1.
-    #if defined(__APPLE__)
+    #ifdef __linux__
+        int val = 0;
+        asm volatile("mrs %0, ID_AA64PFR1_EL1" : "=r"(val));
+        // ID_AA64PFR1_EL1.BT, bits [3:0] = 0b0001 if Branch Target Identification
+        // mechanism implemented.
+        if ((val & 0xF) != 0x1)
+          return false;
+    #elif defined(__APPLE__)
         // On Apple platforms, we need to check a sysctl.
         int32_t val = 0;
         size_t size = sizeof(val);