Fix make_fcontext/jump_fcontext with SHSTK enabled

Sync Zend/asm/*_x86_64_sysv_elf_gas.S with upstream

Author: arnaud-lb

Zend/asm/jump_x86_64_sysv_elf_gas.S

@@ -64,14 +64,6 @@ jump_fcontext:
     movq  %rbx, 0x30(%rsp)  /* save RBX */
     movq  %rbp, 0x38(%rsp)  /* save RBP */
 
-#if BOOST_CONTEXT_SHADOW_STACK
-    /* grow the stack to reserve space for shadow stack pointer(SSP) */
-    leaq  -0x8(%rsp), %rsp
-    /* read the current SSP and store it */
-    rdsspq  %rcx
-    movq  %rcx, (%rsp)
-#endif
-
 #if BOOST_CONTEXT_SHADOW_STACK
     /* grow the stack to reserve space for shadow stack pointer(SSP) */
     leaq  -0x8(%rsp), %rsp

Zend/asm/make_x86_64_sysv_elf_gas.S

@@ -88,35 +88,6 @@ make_fcontext:
     /* will be entered after context-function returns */
     movq  %rcx, 0x38(%rax)
 
-#if BOOST_CONTEXT_SHADOW_STACK
-    /* Populate the shadow stack and normal stack */
-    /* get original SSP */
-    rdsspq  %r8
-    /* restore new shadow stack */
-    rstorssp  -0x8(%r9)
-    /* save the restore token on the original shadow stack */
-    saveprevssp
-    /* push the address of "jmp trampoline" to the new shadow stack */
-    /* as well as the stack */
-    call  1f
-    jmp  trampoline
-1:
-    /* save address of "jmp trampoline" as return-address */
-    /* for context-function */
-    pop 0x38(%rax)
-    /* Get the new SSP.  */
-    rdsspq  %r9
-    /* restore original shadow stack */
-    rstorssp  -0x8(%r8)
-    /* save the restore token on the new shadow stack.  */
-    saveprevssp
-
-    /* reserve space for the new SSP */
-    leaq  -0x8(%rax), %rax
-    /* save the new SSP to this fcontext */
-    movq  %r9, (%rax)
-#endif
-
 #if BOOST_CONTEXT_SHADOW_STACK
     /* Populate the shadow stack */