Use v4 DWARF on riscv64

[jjhelmus]

Use DWARF v4 on riscv64 to avoid relocations that the GNU linker from Debian Buster does not support.

[jjhelmus]

This addresses the unsupported relocation types when linking that have existed since the switch to LLVM with riscv in #1101.

Specifically these types of warnings are no longer present as DWARF v4 does not uses these types of relocations.

cpython-3.13> /usr/bin/riscv64-linux-gnu-ld: Objects/listobject.o: unsupported relocation type 0x3c
cpython-3.13> /usr/bin/riscv64-linux-gnu-ld: Objects/listobject.o: unsupported relocation type 0x3d

Unfortunately this does not address the build failure on 3.13 freethreaded+debug that started with the update to OpenSSL 3.5.7, #1144.

2026-06-10T22:07:32.1897413Z cpython-3.13> ciphercommon.c:(.text+0x1534): relocation truncated to fit: R_RISCV_JAL against symbol `ERR_set_error' defined in .text section in /tools/deps/lib/libcrypto.a(libcrypto-lib-err_blocks.o)

[jjhelmus]

This is no longer needed now that GCC is used for riscv64 cross compiling, #1150. This option should be revisited if LLVM is once again used.