Minimal reproducers (for target-arch):

extern
__attribute__((target("arch=+zba")))
__attribute__((target("arch=+zbb")))
void foo(void);

extern
__attribute__((target("arch=+zbb")))
__attribute__((target("arch=+zbb")))
void bar(void);

The ICE is a bug.
If multiple target-arch attributes should not be allowed,
then an error message is the right solution.

Allowing multiple target-X attributes is problematic, as can be seen for baz().
I.e., does the second attribute amend or replace the previous one?
However, accepting multiple target-X attributes if they are equal (like for bar)
could be done.

The assertion was added in the GCC 14 cycle (commit 9941f0295a1).
GCC 14 and 15 are affected. GCC 13 is not affected (we don't have RISC-V target-arch
attributes in GCC 13).

The ICE looks like this:
$ riscv64-unknown-linux-gnu-gcc bar.c -c
bar.c:4:1: internal compiler error: in riscv_func_target_put, at common/config/riscv/riscv-common.cc:521
    4 | void foo(void);
      | ^~~~
0xc15306 riscv_func_target_put(tree_node*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)
        /home/cm/src/gcc/riscv-mainline/gcc/common/config/riscv/riscv-common.cc:521
0x18234d3 riscv_process_target_attr
        /home/cm/src/gcc/riscv-mainline/gcc/config/riscv/riscv-target-attr.cc:370
0x182334c riscv_process_target_attr
        /home/cm/src/gcc/riscv-mainline/gcc/config/riscv/riscv-target-attr.cc:314
0x182363d riscv_option_valid_attribute_p(tree_node*, tree_node*, tree_node*, int)
        /home/cm/src/gcc/riscv-mainline/gcc/config/riscv/riscv-target-attr.cc:389
0xd560ee handle_target_attribute
        /home/cm/src/gcc/riscv-mainline/gcc/c-family/c-attribs.cc:5915
0xc24d04 decl_attributes(tree_node**, tree_node*, int, tree_node*)
        /home/cm/src/gcc/riscv-mainline/gcc/attribs.cc:900
0xc2bbed c_decl_attributes
        /home/cm/src/gcc/riscv-mainline/gcc/c/c-decl.cc:5501
0xc43b77 start_decl(c_declarator*, c_declspecs*, bool, tree_node*, bool, unsigned int*)
        /home/cm/src/gcc/riscv-mainline/gcc/c/c-decl.cc:5647
0xcb4d73 c_parser_declaration_or_fndef
        /home/cm/src/gcc/riscv-mainline/gcc/c/c-parser.cc:2773
0xcc158b c_parser_external_declaration
        /home/cm/src/gcc/riscv-mainline/gcc/c/c-parser.cc:2053
0xcc1fb5 c_parser_translation_unit
        /home/cm/src/gcc/riscv-mainline/gcc/c/c-parser.cc:1907
0xcc1fb5 c_parse_file()
        /home/cm/src/gcc/riscv-mainline/gcc/c/c-parser.cc:27303
0xd3b9c1 c_common_parse_file()
        /home/cm/src/gcc/riscv-mainline/gcc/c-family/c-opts.cc:1322