lib9: remove getcallerpc implementations

These make no sense and are not really needed at all.
Add a best-effort attempt to get at the gcc/clang macro
in lib9.h, but if it fails, no big deal.

Fixes #324.

include/libc.h

@@ -385,6 +385,9 @@ extern	int	exitcode(char*);
 extern	void	exits(char*);
 extern	double	frexp(double, int*);
 extern	ulong	getcallerpc(void*);
+#if defined(__GNUC__) || defined(__clang__)
+#define getcallerpc(x) ((ulong)__builtin_return_address(0))
+#endif
 extern	char*	p9getenv(char*);
 extern	int	p9putenv(char*, char*);
 extern	int	getfields(char*, char**, int, int, char*);

src/lib9/getcallerpc-386.c

@@ -1,7 +0,0 @@
-#include <lib9.h>
-
-ulong
-getcallerpc(void *x)
-{
-	return (((ulong*)(x))[-1]);
-}

src/lib9/getcallerpc-arm.c

@@ -1,8 +0,0 @@
-#include <lib9.h>
-
-ulong
-getcallerpc(void *x)
-{
-	return ((ulong*)x)[-2];
-}
-

src/lib9/getcallerpc-arm64.c

@@ -1,8 +0,0 @@
-#include <lib9.h>
-
-ulong
-getcallerpc(void *x)
-{
-	return ((ulong*)x)[-2];
-}
-

src/lib9/getcallerpc-mips.c

@@ -1,8 +0,0 @@
-#include <lib9.h>
-
-ulong
-getcallerpc(void *x)
-{
-	return ((ulong*)x)[-2];
-}
-

src/lib9/getcallerpc-power.c

@@ -1,11 +0,0 @@
-#include <lib9.h>
-
-ulong
-getcallerpc(void *x)
-{
-	ulong *lp;
-
-	lp = x;
-
-	return lp[-1];
-}

src/lib9/getcallerpc-sun4u.s

@@ -1,5 +0,0 @@
-.text
-.globl getcallerpc
-getcallerpc:
-	retl
-	or %o7, %r0, %o0

src/lib9/getcallerpc-x86_64.c

@@ -1,7 +0,0 @@
-#include <lib9.h>
-
-ulong
-getcallerpc(void *x)
-{
-	return (((ulong*)(x))[-1]);
-}

src/lib9/mkfile

@@ -104,7 +104,7 @@ LIB9OFILES=\
 	fcallfmt.$O\
 	frand.$O\
 	get9root.$O\
-	getcallerpc-$OBJTYPE.$O\
+	getcallerpc.$O\
 	getenv.$O\
 	getfields.$O\
 	getnetconn.$O\