ld: make ELF binaries with no shared library dependencies static binaries

$ file $GOROOT/bin/{godoc,goyacc}
/home/rsc/g/go/bin/godoc:  ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), not strpped
/home/rsc/g/go/bin/goyacc: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, not stripped
$

Fixes #1758.

R=iant
CC=golang-dev
https://golang.org/cl/4428079

src/cmd/ld/go.c

@@ -454,6 +454,7 @@ loaddynimport(char *file, char *pkg, char *p, int n)
 		if(strcmp(name, "_") == 0 && strcmp(def, "_") == 0) {
 			// allow #pragma dynimport _ _ "foo.so"
 			// to force a link of foo.so.
+			havedynamic = 1;
 			adddynlib(lib);
 			continue;
 		}
@@ -468,6 +469,7 @@ loaddynimport(char *file, char *pkg, char *p, int n)
 			s->dynimpname = def;
 			s->dynimpvers = q;
 			s->type = SDYNIMPORT;
+			havedynamic = 1;
 		}
 	}
 	return;

src/cmd/ld/lib.c

@@ -259,6 +259,18 @@ loadlib(void)
 			Bprint(&bso, "%5.2f autolib: %s (from %s)\n", cputime(), library[i].file, library[i].objref);
 		objfile(library[i].file, library[i].pkg);
 	}
+	
+	// We've loaded all the code now.
+	// If there are no dynamic libraries needed, gcc disables dynamic linking.
+	// Because of this, glibc's dynamic ELF loader occasionally (like in version 2.13)
+	// assumes that a dynamic binary always refers to at least one dynamic library.
+	// Rather than be a source of test cases for glibc, disable dynamic linking
+	// the same way that gcc would.
+	//
+	// Exception: on OS X, programs such as Shark only work with dynamic
+	// binaries, so leave it enabled on OS X (Mach-O) binaries.
+	if(!havedynamic && HEADTYPE != Hdarwin)
+		debug['d'] = 1;
 }
 
 /*

src/cmd/ld/lib.h

@@ -122,6 +122,7 @@ EXTERN	char*	outfile;
 EXTERN	int32	nsymbol;
 EXTERN	char*	thestring;
 EXTERN	int	ndynexp;
+EXTERN	int	havedynamic;
 
 EXTERN	Segment	segtext;
 EXTERN	Segment	segdata;