When cross-compiling, you must specify a C cross-compiler for cgo to
use. You can do this by setting the generic CC_FOR_TARGET or the
more specific CC_FOR_${GOOS}_${GOARCH} (for example, CC_FOR_linux_arm)
environment variable when building the toolchain using make.bash,
or you can set the CC environment variable any time you run the go tool.

The CXX_FOR_TARGET, CXX_FOR_${GOOS}_${GOARCH}, and CXX

0000070 2e 4c 6e a5 60 45 02 62 81 95 b6 94 9e 9e 77 e7
0000080 d0 43 b6 f8 71 df 96 3c e7 a4 69 ce bf cf e9 79
0000090 ce ef 79 3f bf f1 31 db b6 bb 31 76 92 e7 f3 07
00000a0 8b fc 9c ca cc 08 cc cb cc 5e d2 1c 88 d9 7e bb
00000b0 4f bb 3a 3f 75 f1 5d 7f 8f c2 68 67 77 8f 25 ff
00000c0 84 e2 93 2d ef a4 95 3d 71 4e 2c b9 b0 87 c3 be
00000d0 3d f8 a7 60 24 61 c5 ef ae 9e c8 6c 6d 4e 69 c8

	"PW": arm.C_WBIT | arm.C_PBIT,
	"WP": arm.C_WBIT | arm.C_PBIT,
}

var armSCOND = map[string]uint8{
	"EQ":  arm.C_SCOND_EQ,
	"NE":  arm.C_SCOND_NE,
	"CS":  arm.C_SCOND_HS,
	"HS":  arm.C_SCOND_HS,
	"CC":  arm.C_SCOND_LO,
	"LO":  arm.C_SCOND_LO,
	"MI":  arm.C_SCOND_MI,
	"PL":  arm.C_SCOND_PL,
	"VS":  arm.C_SCOND_VS,
	"VC":  arm.C_SCOND_VC,
	"HI":  arm.C_SCOND_HI,
	"LS":  arm.C_SCOND_LS,
	"GE":  arm.C_SCOND_GE,

			arm64SpecialOperand[opd.String()] = opd
		}

		// Handle some special cases.
		specialMapping := map[string]arm64.SpecialOperand{
			// The internal representation of CS(CC) and HS(LO) are the same.
			"CS": arm64.SPOP_HS,
			"CC": arm64.SPOP_LO,
		}
		for s, opd := range specialMapping {
			arm64SpecialOperand[s] = opd
		}
	}
	if opd, ok := arm64SpecialOperand[name]; ok {
		return opd
	}

//
// checkGCCBaseCmd confirms that the compiler exists in PATH, returning
// an error if it does not.
func checkGCCBaseCmd() ([]string, error) {
	// Use $CC if set, since that's what the build uses.
	value := os.Getenv("CC")
	if value == "" {
		// Try $GCC if set, since that's what we used to use.
		value = os.Getenv("GCC")
	}
	if value == "" {
		value = defaultCC(goos, goarch)
	}