added compile time intrinsics that allow for modification of the prelude and bss section

tests/bss_override.expected

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+256

tests/bss_override.sl

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+import stdlib/stdlib.sl
+import stdlib/io.sl
+
+:asm persistent-size {
+    lea rax, [rel persistent_end]
+    lea rbx, [rel persistent]
+    sub rax, rbx
+    sub r12, 8
+    mov [r12], rax
+}
+;
+
+word ss
+    # Override BSS to grow the persistent buffer.
+    bss-clear
+    "align 16" bss-append
+    "dstack: resb DSTK_BYTES" bss-append
+    "dstack_top:" bss-append
+    "align 16" bss-append
+    "rstack: resb RSTK_BYTES" bss-append
+    "rstack_top:" bss-append
+    "align 16" bss-append
+    "print_buf: resb PRINT_BUF_BYTES" bss-append
+    "print_buf_end:" bss-append
+    "align 16" bss-append
+    "persistent: resb 256" bss-append
+    "persistent_end:" bss-append
+    "align 16" bss-append
+    "list_capture_sp: resq 1" bss-append
+    "list_capture_tmp: resq 1" bss-append
+    "list_capture_stack: resq 1024" bss-append
+end
+
+word main
+    persistent-size
+    print
+end
+compile-time ss

tests/bss_override.test

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+python main.py tests/bss_override.sl -o /tmp/bss_override > /dev/null && /tmp/bss_override