[crt] Remove __USER_LABEL_PREFIX__

The .init_array code is ELF specific. For ELF platforms,
`__USER_LABEL_PREFIX__` is defined as "". Make the simplification
so that downstream ELF targets can build this file even if
`__USER_LABEL_PREFIX__` is undefined.

Reviewed By: barannikov88

Differential Revision: https://reviews.llvm.org/D147093

Author: MaskRay

compiler-rt/lib/crt/crtbegin.c

@@ -50,25 +50,25 @@ __attribute__((section(".init_array"),
                used)) static void (*__init)(void) = __do_init;
 #elif defined(__i386__) || defined(__x86_64__)
 __asm__(".pushsection .init,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_init\n\t"
-    ".popsection");
+        "call __do_init\n\t"
+        ".popsection");
 #elif defined(__riscv)
 __asm__(".pushsection .init,\"ax\",%progbits\n\t"
-        "call " __USER_LABEL_PREFIX__ "__do_init\n\t"
+        "call __do_init\n\t"
         ".popsection");
 #elif defined(__arm__) || defined(__aarch64__)
 __asm__(".pushsection .init,\"ax\",%progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_init\n\t"
-    ".popsection");
+        "bl __do_init\n\t"
+        ".popsection");
 #elif defined(__powerpc__) || defined(__powerpc64__)
 __asm__(".pushsection .init,\"ax\",@progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_init\n\t"
-    "nop\n\t"
-    ".popsection");
+        "bl __do_init\n\t"
+        "nop\n\t"
+        ".popsection");
 #elif defined(__sparc__)
 __asm__(".pushsection .init,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_init\n\t"
-    ".popsection");
+        "call __do_init\n\t"
+        ".popsection");
 #else
 #error "crtbegin without .init_fini array unimplemented for this architecture"
 #endif // CRT_HAS_INITFINI_ARRAY
@@ -103,25 +103,25 @@ __attribute__((section(".fini_array"),
                used)) static void (*__fini)(void) = __do_fini;
 #elif defined(__i386__) || defined(__x86_64__)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_fini\n\t"
-    ".popsection");
+        "call __do_fini\n\t"
+        ".popsection");
 #elif defined(__arm__) || defined(__aarch64__)
 __asm__(".pushsection .fini,\"ax\",%progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_fini\n\t"
-    ".popsection");
+        "bl __do_fini\n\t"
+        ".popsection");
 #elif defined(__powerpc__) || defined(__powerpc64__)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_fini\n\t"
-    "nop\n\t"
-    ".popsection");
+        "bl __do_fini\n\t"
+        "nop\n\t"
+        ".popsection");
 #elif defined(__riscv)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-        "call " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+        "call __do_fini\n\t"
         ".popsection");
 #elif defined(__sparc__)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_fini\n\t"
-    ".popsection");
+        "call __do_fini\n\t"
+        ".popsection");
 #else
 #error "crtbegin without .init_fini array unimplemented for this architecture"
 #endif  // CRT_HAS_INIT_FINI_ARRAY