[AArch64] Assembly failure with -save-temps when a function name matches a register name

I found an AArch64 assembly failure in Clang/LLVM when -save-temps is used
and a function name overlaps with an AArch64 register name.

This appears to be an ambiguity issue in the emitted assembly: the symbol name
is parsed as a register name by the assembler rather than as a function symbol.

Minimal reproducer:

#include <stdio.h>

void xzr(void) {
    printf("Hello world\n");
}

int main(void) {
    xzr();
    return 0;
}

Command line:

$ clang-22 --target=aarch64-linux-gnu xzr.c --save-temps

Actual result:

xzr.s:44:5: error: expected label or encodable integer pc offset
        bl      xzr
                ^

The emitted assembly contains:

bl      xzr

Here, xzr is the intended function name, but the assembler appears to parse
xzr as a register name rather than as a branch target symbol. I observed a
similar failure when the b instruction is emitted, for example:

b       xzr

Expected result:
The program should compile successfully, and the emitted assembly should
unambiguously refer to the function symbol.

Possible fixes:
One possible fix would be to quote ambiguous symbol names in the emitted
assembly, for example:

bl      "xzr"

In my testing, emitting double quotes around such symbols resolves the
ambiguity. I tested this quoting-based approach across Clang versions 14
through 22 and did not observe compatibility issues.

Alternatively, the assembler/tokenizer could treat the operand of bl and
b as a symbol/branch target rather than as a register token in this context.

Additional observations:

• I observed this issue across Clang versions 14 through 22.
• The exact number of affected identifiers differs by version, but I found
  approximately 279 to 344 failing cases depending on the Clang version.
• The affected identifiers appear to correspond mostly or entirely to AArch64
  register names.
• This issue appears to be an assembly ambiguity issue caused by unquoted
  symbol names colliding with architecture-specific register names.

Reproduce the failure with the provided xzr.c example and clang-22 --target=aarch64-linux-gnu xzr.c --save-temps, then inspect the emitted bl xzr and b xzr operands. Trace the AArch64 assembly emission and assembler parsing involved; done means the program compiles successfully and branch targets that match register names are unambiguous.