引用自：Metal-Shading-Language-Specification.pdf(第14页)
Compiler Options Controlling the Language Version
The following option controls the version of the unified graphics and computing language
accepted by the compiler:
-std=
Determine the language revision to use. A value for this option must be provided, which must
be one of:
// iOS
! ios-metal1.0: Support the unified graphics and computing language revision 1.0 programs
for iOS 8.
! ios-metal1.1: Support the unified graphics and computing language revision 1.1 programs
for iOS 9.
! ios-metal1.2: Support the unified graphics and computing language revision 1.2 programs
for iOS 10.
! ios-metal2.0: Support the unified graphics and computing language revision 2.0 programs
for iOS 11.
! ios-metal2.1: Support the unified graphics and computing language revision 2.1 programs
for iOS 12.
! ios-metal2.2: Support the unified graphics and computing language revision 2.2 programs
for iOS 13.
! ios-metal2.3: Support the unified graphics and computing language revision 2.3 programs
for iOS 14.
! ios-metal2.4: Support the unified graphics and computing language revision 2.4 programs
for iOS 15.
// MacOS
! macos-metal1,1 or osx-metal1.1: Support the unified graphics and computing language
revision 1.1 programs for macOS 10.11.
! macos-metal1.2 or osx-metal1.2: Support the unified graphics and computing language
revision 1.2 programs for macOS 10.12.
! macos-metal2.0 or osx-metal2.0: Support the unified graphics and computing language
revision 2.0 programs for macOS 10.13.
! macos-metal2.1: Support the unified graphics and computing language revision 2.1
programs for macOS 10.14.
! macos-metal2.2: Support the unified graphics and computing language revision 2.2
programs for macOS 10.15.
! macos-metal2.3: Support the unified graphics and computing language revision 2.3
programs for macOS 11.0.
! macos-metal2.4: Support the unified graphics and computing language revision 2.4
programs for macOS 12.0.
Note that macos-* is available in macOS10.13 SDK and later.
