Rename entrypoint to _start

This matches the default.

src/aarch64.ld

@@ -1,4 +1,4 @@
-ENTRY(ustart)
+ENTRY(_start)
 OUTPUT_FORMAT("elf64-littleaarch64", "elf64-littleaarch64", "elf64-littleaarch64")
 
 SECTIONS {

src/aarch64.rs

@@ -20,8 +20,8 @@ static MAP: Map = Map {
 
 core::arch::global_asm!(
     "
-    .globl ustart
-    ustart:
+    .globl _start
+    _start:
     // Setup a stack.
     ldr x8, ={number}
     ldr x0, ={fd}

src/i686.ld

@@ -1,4 +1,4 @@
-ENTRY(ustart)
+ENTRY(_start)
 OUTPUT_FORMAT(elf32-i386)
 
 SECTIONS {

src/i686.rs

@@ -15,9 +15,9 @@ static MAP: Map = Map {
 };
 
 core::arch::global_asm!(
-"
-    .globl ustart
-    ustart:
+    "
+    .globl _start
+    _start:
     # Setup a stack.
     mov eax, {number}
     mov ebx, {fd}

src/x86_64.ld

@@ -1,4 +1,4 @@
-ENTRY(ustart)
+ENTRY(_start)
 OUTPUT_FORMAT(elf64-x86-64)
 
 SECTIONS {

src/x86_64.rs

@@ -17,8 +17,8 @@ static MAP: Map = Map {
 
 core::arch::global_asm!(
     "
-    .globl ustart
-    ustart:
+    .globl _start
+    _start:
     # Setup a stack.
     mov rax, {number}
     mov rdi, {fd}