GPU: extend two existing OpenCL device workarounds to Metal

Both of these already exist for OpenCL, for reasons that apply unchanged to
Metal.

The processing settings block in GPUSettingsList.h is skipped for OpenCL because
it declares std::string and std::vector members, which GPUSettings.h explicitly
does not include for device code. Metal needs the same exclusion. These configs
are host-side only: GPUParam carries GPUSettingsRec and GPUSettingsParam, and the
processing settings appear only as pointer arguments to host methods, so nothing
transferred changes shape.

GPUCommonBitSet already carries an extra constructor for OpenCL's __constant.
Metal needs the opposite: MSL will not use a user-declared copy constructor to
build an object in the constant address space, which is where GPUconstexpr()
arrays of bitset live, and leaving the copy constructor implicit makes them
constructible again. That one line accounted for 84 of the remaining
diagnostics, across DetID and GlobalTrackID.

Metal translation unit: 136 errors to 27.

Author: ktf

GPU/GPUTracking/Definitions/GPUSettingsList.h

@@ -221,7 +221,7 @@ AddSubConfig(GPUSettingsRecDynamic, dyn)
 AddHelp("help", 'h')
 EndConfig()
 
-#ifndef __OPENCL__
+#if !defined(__OPENCL__) && !defined(__METAL__) // these use std::string / std::vector, which device code does not have
 // Parameters that might affect the RTC code (if these change, the cache cannot be used)
 BeginSubConfig(GPUSettingsProcessingRTC, rtc, configStandalone.proc, "RTC", 0, "Processing settings", proc_rtc)
 AddOption(cacheOutput, bool, false, "", 0, "Cache RTC compilation results")
@@ -428,7 +428,7 @@ AddSubConfig(GPUSettingsProcessingNNclusterizer, nn)
 AddSubConfig(GPUSettingsProcessingScaling, scaling)
 AddHelp("help", 'h')
 EndConfig()
-#endif // __OPENCL__
+#endif // !__OPENCL__ && !__METAL__
 
 #ifndef GPUCA_GPUCODE_DEVICE
 // Light settings concerning the event display (can be changed without rebuilding vertices)

GPU/Utils/GPUCommonBitSet.h

@@ -37,7 +37,12 @@ class bitset
 
  public:
   GPUdDefault() constexpr bitset() = default;
+#ifndef __METAL__
+  // MSL will not use a user-declared copy constructor to build an object in the
+  // constant address space, where GPUconstexpr() arrays of bitset live. Leaving
+  // it implicit is what makes those arrays constructible.
   GPUdDefault() constexpr bitset(const bitset&) = default;
+#endif
 #ifdef __OPENCL__
   GPUdDefault() constexpr bitset(const __constant bitset&) = default;
 #endif // __OPENCL__