compiler, libgo: support bootstrapping gc compiler

In the Go 1.21 release the package internal/profile imports
internal/lazyregexp.  That works when bootstrapping with Go 1.17,
because that compiler has internal/lazyregep and permits importing it.
We also have internal/lazyregexp in libgo, but since it is not installed
it is not available for importing.  This CL adds internal/lazyregexp
to the list of internal packages that are installed for bootstrapping.

The Go 1.21, and earlier, releases have a couple of functions in
the internal/abi package that are always fully intrinsified.
The gofrontend recognizes and intrinsifies those functions as well.
However, the gofrontend was also building function descriptors
for references to the functions without calling them, which
failed because there was nothing to refer to.  That is OK for the
gc compiler, which guarantees that the functions are only called,
not referenced.  This CL arranges to not generate function descriptors
for these functions.

For golang/go#60913

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/504798

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-195060166e6045408a2cb95e6aa88c6f0b98f20b
+68a756b6aadc901534cfddddad2b1e73fae9e34f
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/expressions.cc

@@ -12272,7 +12272,8 @@ Call_expression::intrinsify(Gogo* gogo,
           return Runtime::make_call(code, loc, 3, a1, a2, a3);
         }
     }
-  else if (package == "internal/abi")
+  else if (package == "internal/abi"
+	   || package == "bootstrap/internal/abi") // for bootstrapping gc
     {
       if (is_method)
 	return NULL;

gcc/go/gofrontend/gogo.cc

@@ -3296,6 +3296,9 @@ class Create_function_descriptors : public Traverse
   int
   expression(Expression**);
 
+  static bool
+  skip_descriptor(Gogo* gogo, const Named_object*);
+
  private:
   Gogo* gogo_;
 };
@@ -3306,6 +3309,9 @@ class Create_function_descriptors : public Traverse
 int
 Create_function_descriptors::function(Named_object* no)
 {
+  if (Create_function_descriptors::skip_descriptor(this->gogo_, no))
+    return TRAVERSE_CONTINUE;
+
   if (no->is_function()
       && no->func_value()->enclosing() == NULL
       && !no->func_value()->is_method()
@@ -3393,6 +3399,28 @@ Create_function_descriptors::expression(Expression** pexpr)
   return TRAVERSE_CONTINUE;
 }
 
+// The gc compiler has some special cases that it always compiles as
+// intrinsics.  For those we don't want to generate a function
+// descriptor, as there will be no code for it to refer to.
+
+bool
+Create_function_descriptors::skip_descriptor(Gogo* gogo,
+					     const Named_object* no)
+{
+  const std::string& pkgpath(no->package() == NULL
+			     ? gogo->pkgpath()
+			     : no->package()->pkgpath());
+
+  // internal/abi is the standard library package,
+  // bootstrap/internal/abi is the name used when bootstrapping the gc
+  // compiler.
+
+  return ((pkgpath == "internal/abi"
+	   || pkgpath == "bootstrap/internal/abi")
+	  && (no->name() == "FuncPCABI0"
+	      || no->name() == "FuncPCABIInternal"));
+}
+
 // Create function descriptors as needed.  We need a function
 // descriptor for all exported functions and for all functions that
 // are referenced without being called.
@@ -3414,7 +3442,8 @@ Gogo::create_function_descriptors()
       if (no->is_function_declaration()
 	  && !no->func_declaration_value()->type()->is_method()
 	  && !Linemap::is_predeclared_location(no->location())
-	  && !Gogo::is_hidden_name(no->name()))
+	  && !Gogo::is_hidden_name(no->name())
+	  && !Create_function_descriptors::skip_descriptor(this, no))
 	fndecls.push_back(no);
     }
   for (std::vector<Named_object*>::const_iterator p = fndecls.begin();

libgo/Makefile.am

@@ -417,6 +417,7 @@ toolexeclibgounicode_DATA = \
 # Some internal packages are needed to bootstrap the gc toolchain.
 toolexeclibgointernaldir = $(toolexeclibgodir)/internal
 toolexeclibgointernal_DATA = \
+	internal/lazyregexp.gox \
 	internal/reflectlite.gox \
 	internal/unsafeheader.gox
 

libgo/Makefile.in

@@ -885,6 +885,7 @@ toolexeclibgounicode_DATA = \
 # Some internal packages are needed to bootstrap the gc toolchain.
 toolexeclibgointernaldir = $(toolexeclibgodir)/internal
 toolexeclibgointernal_DATA = \
+	internal/lazyregexp.gox \
 	internal/reflectlite.gox \
 	internal/unsafeheader.gox
 

libgo/go/internal/abi/abi.go

@@ -17,10 +17,7 @@ package abi
 // compile-time error.
 //
 // Implemented as a compile intrinsic.
-func FuncPCABI0(f any) uintptr {
-	// The compiler should remove all calls.
-	panic("FuncPCABI0")
-}
+func FuncPCABI0(f any) uintptr
 
 // FuncPCABIInternal returns the entry PC of the function f. If f is a
 // direct reference of a function, it must be defined as ABIInternal.
@@ -29,7 +26,4 @@ func FuncPCABI0(f any) uintptr {
 // the behavior is undefined.
 //
 // Implemented as a compile intrinsic.
-func FuncPCABIInternal(f any) uintptr {
-	// The compiler should remove all calls.
-	panic("FuncPCABIInternal")
-}
+func FuncPCABIInternal(f any) uintptr