Add Go support to default_target_compile

This adds Go support to default_target_compile.  This comes from this
gdb patch:

    commit a766d390bb857383a5f9ae80a102e1f8705f4c2e
    Author: Doug Evans <dje@google.com>
    Date:   Wed Apr 25 14:07:23 2012 +0000

		Initial pass at Go language support.

ChangeLog

@@ -1,3 +1,10 @@
+2020-06-19  Tom Tromey  <tromey@adacore.com>
+
+	* doc/dejagnu.texi (target_compile procedure): Document Go
+	additions.
+	* lib/target.exp (default_target_compile): Handle Go.
+	* lib/libgloss.exp (find_go, find_go_linker): New procs.
+
 2020-06-19  Tom Tromey  <tromey@adacore.com>
 
 	* doc/dejagnu.texi (target_compile procedure): Document rust

doc/dejagnu.texi

@@ -4564,6 +4564,8 @@ Use a compiler for the D language.
 Use a compiler for Fortran 77.
 @item f90
 Use a compiler for Fortran 90.
+@item go
+Use a compiler for Go.
 @item rust
 Use a compiler for Rust.
 @end table
@@ -4672,6 +4674,12 @@ compiler will be used and the @code{compiler} option ignored.
 @item F90_FOR_TARGET
 Override Fortran 90 compiler.  If the @code{f90} option is given, this
 compiler will be used and the @code{compiler} option ignored.
+@item GO_FOR_TARGET
+Override Go compiler.  If the @code{go} option is given, this
+compiler will be used and the @code{compiler} option ignored.
+@item GO_LD_FOR_TARGET
+Override Go linker.  If the @code{go} option is given, this
+linker will be used.
 @item RUSTC_FOR_TARGET
 Override Rust compiler.  If the @code{rust} option is given, this
 compiler will be used and the @code{compiler} option ignored.

lib/libgloss.exp

@@ -765,6 +765,30 @@ proc find_gnatmake {} {
     return $CC
 }
 
+proc find_go {} {
+    global tool_root_dir
+
+    set GO ""
+
+    if {![is_remote host]} {
+	set file [lookfor_file $tool_root_dir gccgo]
+	if { $file ne "" } {
+	    set root [file dirname $file]
+	    set GO "$file -B$root/gcc/"
+	}
+    }
+
+    if { $GO eq "" } {
+	set GO [transform gccgo]
+    }
+
+    return $GO
+}
+
+proc find_go_linker {} {
+    return [find_go]
+}
+
 proc find_rustc {} {
     global tool_root_dir
     if {![is_remote host]} {

lib/target.exp

@@ -400,6 +400,26 @@ proc default_target_compile {source destfile type options} {
 	    }
 	}
 
+	if { $i eq "go" } {
+	    set compiler_type "go"
+	    if {[board_info $dest exists goflags]} {
+		append add_flags " [board_info $dest goflags]"
+	    }
+	    if {[board_info $dest exists gocompiler]} {
+		set compiler [board_info $dest gocompiler]
+	    } else {
+		set compiler [find_go]
+	    }
+	    if {[board_info $dest exists golinker]} {
+		set linker [board_info $dest golinker]
+	    } else {
+		set linker [find_go_linker]
+	    }
+	    if {[board_info $dest exists golinker_opts_order]} {
+		set linker_opts_order [board_info $dest golinker_opts_order]
+	    }
+	}
+
 	if { $i eq "rust" } {
 	    set compiler_type "rust"
 	    if {[board_info $dest exists rustflags]} {
@@ -472,6 +492,8 @@ proc default_target_compile {source destfile type options} {
     global F77_FOR_TARGET
     global F90_FOR_TARGET
     global GNATMAKE_FOR_TARGET
+    global GO_FOR_TARGET
+    global GO_LD_FOR_TARGET
     global RUSTC_FOR_TARGET
 
     if {[info exists GNATMAKE_FOR_TARGET]} {
@@ -510,6 +532,15 @@ proc default_target_compile {source destfile type options} {
 	}
     }
 
+    if { $compiler_type eq "go" } {
+	if {[info exists GO_FOR_TARGET]} {
+	    set compiler $GO_FOR_TARGET
+	}
+	if {[info exists GO_LD_FOR_TARGET]} {
+	    set linker $GO_LD_FOR_TARGET
+	}
+    }
+
     if {[info exists RUSTC_FOR_TARGET]} {
 	if {$compiler_type eq "rust"} {
 	    set compiler $RUSTC_FOR_TARGET