std: Add elf.EM, coff.MachineType to Target.CPU.Arch conversions

target.Arch already supports finding the correct encoding for either
target, so being able to do the inverse has use cases for when parsing
files of an unknown target (i.e. for zar).

lib/std/coff.zig

@@ -62,6 +62,21 @@ pub const MachineType = enum(u16) {
     Thumb = 0x1c2,
     /// MIPS little-endian WCE v2
     WCEMIPSV2 = 0x169,
+
+    pub fn toTargetCpuArch(machine_type: MachineType) ?std.Target.Cpu.Arch {
+        return switch (machine_type) {
+            .ARM => .arm,
+            .POWERPC => .powerpc,
+            .RISCV32 => .riscv32,
+            .Thumb => .thumb,
+            .I386 => .i386,
+            .ARM64 => .aarch64,
+            .RISCV64 => .riscv64,
+            .X64 => .x86_64,
+            // there's cases we don't (yet) handle
+            else => null,
+        };
+    }
 };
 
 // OptionalHeader.magic values

lib/std/elf.zig

@@ -1481,6 +1481,36 @@ pub const EM = enum(u16) {
     _BPF = 247,
 
     _,
+
+    pub fn toTargetCpuArch(em: EM) ?std.Target.Cpu.Arch {
+        return switch (em) {
+            ._AVR => .avr,
+            ._MSP430 => .msp430,
+            ._ARC => .arc,
+            ._ARM => .arm,
+            ._HEXAGON => .hexagon,
+            ._68K => .m68k,
+            ._MIPS => .mips,
+            ._MIPS_RS3_LE => .mipsel,
+            ._PPC => .powerpc,
+            ._SPARC => .sparc,
+            ._386 => .i386,
+            ._XCORE => .xcore,
+            ._CSR_KALIMBA => .kalimba,
+            ._LANAI => .lanai,
+            ._AARCH64 => .aarch64,
+            ._PPC64 => .powerpc64,
+            ._RISCV => .riscv64,
+            ._X86_64 => .x86_64,
+            ._BPF => .bpfel,
+            ._SPARCV9 => .sparcv9,
+            ._S390 => .s390x,
+            ._SPU_2 => .spu_2,
+            // there's many cases we don't (yet) handle, or will never have a
+            // zig target cpu arch equivalent (such as null).
+            else => null,
+        };
+    }
 };
 
 /// Section data should be writable during execution.
@@ -1681,7 +1711,7 @@ pub const R_X86_64_TLSDESC = 36;
 pub const R_X86_64_IRELATIVE = 37;
 /// 64-bit adjust by program base
 pub const R_X86_64_RELATIVE64 = 38;
-/// 39 Reserved was R_X86_64_PC32_BND 
+/// 39 Reserved was R_X86_64_PC32_BND
 /// 40 Reserved was R_X86_64_PLT32_BND
 /// Load from 32 bit signed pc relative offset to GOT entry without REX prefix, relaxable
 pub const R_X86_64_GOTPCRELX = 41;