Backport of LLVM code to fix ARM relocation bug.

Supply a new memory manager for RuntimeDyld that avoids putting ARM code
too far apart.  This is the code from
llvm/llvm-project#71968, copied into our tree
and moved into a new namespace llvm::backport, with minor adjustments to
work on LLVM 12-18.

This should fix the spate of crashes we've been receiving lately from
users on ARM systems.

XXX Ideally the LLVM project will commit this, and then we can resync
with the code in the LLVM 19.x stable branch, instead of using the code
from their PR, before we ship it!

Reported-by: Anthonin Bonnefoy <[email protected]>
Reviewed-by: Anthonin Bonnefoy <[email protected]>
Discussion: https://postgr.es/m/CAO6_Xqr63qj%3DSx7HY6ZiiQ6R_JbX%2B-p6sTPwDYwTWZjUmjsYBg%40mail.gmail.com

Author: macdice

src/backend/jit/llvm/Makefile

@@ -47,7 +47,8 @@ OBJS += \
 	llvmjit.o \
 	llvmjit_error.o \
 	llvmjit_inline.o \
-	llvmjit_wrap.o
+	llvmjit_wrap.o \
+	SectionMemoryManager.o
 
 # Code generation
 OBJS += \