Prevent the use of the hidden attribute for symbols. In particular,
the attribute must not be applied to '__libc'-prefixed symbols to allow
overwriting the dummies defined in dummies.cc by other non-weak
implementations such as those in 'libc_noux.lib.so'.

This attribute is applied inconsistently in
libc/lib/libc/include/libc_private.h anyway.

Also, force i386 to call __libc_sigprocmask via PLT to prevent
R_386_PC32 relocations, which had to change the text segment. Other
architectures do this automatically.

--- src/lib/libc/sys/sys/cdefs.h
+++ src/lib/libc/sys/sys/cdefs.h
@@ -447,7 +447,7 @@
 #if __GNUC_PREREQ__(4, 0)
 #define	__null_sentinel	__attribute__((__sentinel__))
 #define	__exported	__attribute__((__visibility__("default")))
-#define	__hidden	__attribute__((__visibility__("hidden")))
+#define	__hidden
 #else
 #define	__null_sentinel
 #define	__exported
--- src/lib/libc/lib/libc/i386/gen/setjmp.S
+++ src/lib/libc/lib/libc/i386/gen/setjmp.S
@@ -54,7 +54,7 @@
 	pushl	%eax			/* (sigset_t*)oset */
 	pushl	$0			/* (sigset_t*)set  */
 	pushl	$1			/* SIG_BLOCK       */
-	call	__libc_sigprocmask
+	call	__i386_libc_sigprocmask
 	addl	$12,%esp
 	movl	4(%esp),%ecx
 	movl	0(%esp),%edx
@@ -76,7 +76,7 @@
 	leal	28(%edx), %eax
 	pushl	%eax			/* (sigset_t*)set  */
 	pushl	$3			/* SIG_SETMASK     */
-	call	__libc_sigprocmask
+	call	__i386_libc_sigprocmask
 	addl	$12,%esp
 	movl	4(%esp),%edx
 	movl	8(%esp),%eax
--- src/lib/libc/lib/libc/i386/gen/sigsetjmp.S
+++ src/lib/libc/lib/libc/i386/gen/sigsetjmp.S
@@ -63,7 +63,7 @@
 	pushl	%eax			/* (sigset_t*)oset */
 	pushl	$0			/* (sigset_t*)set  */
 	pushl	$1			/* SIG_BLOCK       */
-	call	__libc_sigprocmask
+	call	__i386_libc_sigprocmask
 	addl	$12,%esp
 	movl	4(%esp),%ecx
 2:	movl	0(%esp),%edx
@@ -87,7 +87,7 @@
 	leal	28(%edx), %eax
 	pushl	%eax			/* (sigset_t*)set  */
 	pushl	$3			/* SIG_SETMASK     */
-	call	__libc_sigprocmask
+	call	__i386_libc_sigprocmask
 	addl	$12,%esp
 	movl	4(%esp),%edx
 2:	movl	8(%esp),%eax