um: Avoid longjmp/setjmp symbol clashes with libpthread.a

Building a statically linked UML kernel on a Centos 6.9 host resulted in
the following linking failure (GCC 4.4, glibc-2.12):

/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/libpthread.a(libpthread.o):
In function `siglongjmp':
(.text+0x8490): multiple definition of `longjmp'
arch/x86/um/built-in.o:/local/users/fainelli/openwrt/trunk/build_dir/target-x86_64_musl/linux-uml/linux-4.4.69/arch/x86/um/setjmp_64.S:44:
first defined here
/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/libpthread.a(libpthread.o):
In function `sem_open':
(.text+0x77cd): warning: the use of `mktemp' is dangerous, better use
`mkstemp'
collect2: ld returned 1 exit status
make[4]: *** [vmlinux] Error 1

Adopt a solution similar to the one done for vmap where we define
longjmp/setjmp to be kernel_longjmp/setjmp. In the process, make sure we
do rename the functions in arch/x86/um/setjmp_*.S accordingly.

Fixes: a7df4716d1 ("um: link with -lpthread")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/x86/um/setjmp_32.S

@@ -16,9 +16,9 @@
 
 	.text
 	.align 4
-	.globl setjmp
-	.type setjmp, @function
-setjmp:
+	.globl kernel_setjmp
+	.type kernel_setjmp, @function
+kernel_setjmp:
 #ifdef _REGPARM
 	movl %eax,%edx
 #else
@@ -35,13 +35,13 @@ setjmp:
 	movl %ecx,20(%edx)		# Return address
 	ret
 
-	.size setjmp,.-setjmp
+	.size kernel_setjmp,.-kernel_setjmp
 
 	.text
 	.align 4
-	.globl longjmp
-	.type longjmp, @function
-longjmp:
+	.globl kernel_longjmp
+	.type kernel_longjmp, @function
+kernel_longjmp:
 #ifdef _REGPARM
 	xchgl %eax,%edx
 #else
@@ -55,4 +55,4 @@ longjmp:
 	movl 16(%edx),%edi
 	jmp *20(%edx)
 
-	.size longjmp,.-longjmp
+	.size kernel_longjmp,.-kernel_longjmp

arch/x86/um/setjmp_64.S

@@ -18,9 +18,9 @@
 
 	.text
 	.align 4
-	.globl setjmp
-	.type setjmp, @function
-setjmp:
+	.globl kernel_setjmp
+	.type kernel_setjmp, @function
+kernel_setjmp:
 	pop  %rsi			# Return address, and adjust the stack
 	xorl %eax,%eax			# Return value
 	movq %rbx,(%rdi)
@@ -34,13 +34,13 @@ setjmp:
 	movq %rsi,56(%rdi)		# Return address
 	ret
 
-	.size setjmp,.-setjmp
+	.size kernel_setjmp,.-kernel_setjmp
 
 	.text
 	.align 4
-	.globl longjmp
-	.type longjmp, @function
-longjmp:
+	.globl kernel_longjmp
+	.type kernel_longjmp, @function
+kernel_longjmp:
 	movl %esi,%eax			# Return value (int)
 	movq (%rdi),%rbx
 	movq 8(%rdi),%rsp
@@ -51,4 +51,4 @@ longjmp:
 	movq 48(%rdi),%r15
 	jmp *56(%rdi)
 
-	.size longjmp,.-longjmp
+	.size kernel_longjmp,.-kernel_longjmp