libclc: Add a __builtin to let SPIRV targets select between SW and HW FMA

Reviewer: jenatali jvesely
Differential Revision: https://reviews.llvm.org/D85910

libclc/generic/lib/math/math.h

@@ -40,6 +40,9 @@
 
 #if (defined __AMDGCN__ || defined __R600__) && !defined __HAS_FMAF__
 #define HAVE_HW_FMA32() (0)
+#elif defined CLC_SPIRV || defined CLC_SPIRV64
+bool __attribute__((noinline)) __clc_runtime_has_hw_fma32(void);
+#define HAVE_HW_FMA32() __clc_runtime_has_hw_fma32()
 #else
 #define HAVE_HW_FMA32() (1)
 #endif

libclc/spirv/lib/math/fma.cl

@@ -4,3 +4,8 @@
 #define __CLC_BODY <fma.inc>
 #define __FLOAT_ONLY
 #include <clc/math/gentype.inc>
+
+bool __clc_runtime_has_hw_fma32()
+{
+    return false;
+}

libclc/spirv64/lib/math/fma.cl

@@ -4,3 +4,8 @@
 #define __CLC_BODY <fma.inc>
 #define __FLOAT_ONLY
 #include <clc/math/gentype.inc>
+
+bool __clc_runtime_has_hw_fma32()
+{
+    return false;
+}