tools/nolibc/arch: mark the _start symbol as weak

By doing so we can link together multiple C files that have been compiled
with nolibc and which each have a _start symbol.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/include/nolibc/arch-aarch64.h

@@ -183,6 +183,7 @@ struct sys_stat_struct {
 
 /* startup code */
 asm(".section .text\n"
+    ".weak _start\n"
     ".global _start\n"
     "_start:\n"
     "ldr x0, [sp]\n"              // argc (x0) was in the stack

tools/include/nolibc/arch-arm.h

@@ -176,6 +176,7 @@ struct sys_stat_struct {
 
 /* startup code */
 asm(".section .text\n"
+    ".weak _start\n"
     ".global _start\n"
     "_start:\n"
 #if defined(__THUMBEB__) || defined(__THUMBEL__)

tools/include/nolibc/arch-i386.h

@@ -175,6 +175,7 @@ struct sys_stat_struct {
  *
  */
 asm(".section .text\n"
+    ".weak _start\n"
     ".global _start\n"
     "_start:\n"
     "pop %eax\n"                // argc   (first arg, %eax)

tools/include/nolibc/arch-mips.h

@@ -190,6 +190,7 @@ struct sys_stat_struct {
 
 /* startup code, note that it's called __start on MIPS */
 asm(".section .text\n"
+    ".weak __start\n"
     ".set nomips16\n"
     ".global __start\n"
     ".set    noreorder\n"

tools/include/nolibc/arch-riscv.h

@@ -184,6 +184,7 @@ struct sys_stat_struct {
 
 /* startup code */
 asm(".section .text\n"
+    ".weak _start\n"
     ".global _start\n"
     "_start:\n"
     ".option push\n"

tools/include/nolibc/arch-x86_64.h

@@ -198,6 +198,7 @@ struct sys_stat_struct {
  *
  */
 asm(".section .text\n"
+    ".weak _start\n"
     ".global _start\n"
     "_start:\n"
     "pop %rdi\n"                // argc   (first arg, %rdi)