RISC-V: Relax the order checking for the architecture string

* riscv-toolchain-conventions,
PR, https://github.com/riscv-non-isa/riscv-toolchain-conventions/pull/14
Issue, https://github.com/riscv-non-isa/riscv-toolchain-conventions/issues/11

* Refer to the commit afc41ffb,
RISC-V: Reorder the prefixed extensions which are out of order.

In the past we only allow to reorder the prefixed extensions.  But according
to the PR 14 in the riscv-toolchain-convention, we can also relax the order
checking to allow the whole extensions be written out of orders, including
the single standard extensions and the prefixed multi-letter extensions.
Just that we still need to follow the following rules as usual,

1. prefixed extensions need to be seperated with `_'.
2. prefixed extensions need complete <major>.<minor> version if set.

Please see the details in the march-ok-reorder gas testcase.

Passed the riscv-gnu-toolchain regressions.

bfd/
    * elfxx-riscv.c (enum riscv_prefix_ext_class): Changed RV_ISA_CLASS_UNKNOWN
    to RV_ISA_CLASS_SINGLE, since everything that does not belong to the
    multi-keyword will possible be a single extension for the current parser.
    (parse_config): Likewise.
    (riscv_get_prefix_class): Likewise.
    (riscv_compare_subsets): Likewise.
    (riscv_parse_std_ext): Removed, and merged with riscv_parse_prefixed_ext
    into riscv_parse_extensions.
    (riscv_parse_prefixed_ext): Likewise.
    (riscv_parse_subset): Only need to call riscv_parse_extensions to parse
    both single standard and prefixed extensions.
gas/
    * testsuite/gas/riscv/march-fail-order-std.d: Removed since the relaxed
    order checking.
    * testsuite/gas/riscv/march-fail-order-std.l: Likewise.
    * testsuite/gas/riscv/march-fail-order-x-std.d: Likewise.
    * testsuite/gas/riscv/march-fail-order-z-std.d: Likewise.
    * testsuite/gas/riscv/march-fail-order-zx-std.l: Likewise.
    * testsuite/gas/riscv/march-fail-unknown-std.l: Updated.
    * testsuite/gas/riscv/march-ok-reorder.d: New testcase.

7 files changed, 8 insertions, 14 deletions

diff --git a/gas/testsuite/gas/riscv/march-fail-order-std.d b/gas/testsuite/gas/riscv/march-fail-order-std.d
deleted file mode 100644
index b9c7e09..0000000
--- a/gas/testsuite/gas/riscv/march-fail-order-std.d
+++ /dev/null
@@ -1,3 +0,0 @@
-#as: -march=rv32iamfd
-#source: empty.s
-#error_output: march-fail-order-std.l
diff --git a/gas/testsuite/gas/riscv/march-fail-order-std.l b/gas/testsuite/gas/riscv/march-fail-order-std.l
deleted file mode 100644
index 9e3ce5e..0000000
--- a/gas/testsuite/gas/riscv/march-fail-order-std.l
+++ /dev/null
@@ -1,2 +0,0 @@
-.*Assembler messages:
-.*Error: .*standard ISA extension `m' is not in canonical order
diff --git a/gas/testsuite/gas/riscv/march-fail-order-x-std.d b/gas/testsuite/gas/riscv/march-fail-order-x-std.d
deleted file mode 100644
index 4762f3d..0000000
--- a/gas/testsuite/gas/riscv/march-fail-order-x-std.d
+++ /dev/null
@@ -1,3 +0,0 @@
-#as: -march=rv32i_xargle2p0_mafd
-#source: empty.s
-#error_output: march-fail-order-zx-std.l
diff --git a/gas/testsuite/gas/riscv/march-fail-order-z-std.d b/gas/testsuite/gas/riscv/march-fail-order-z-std.d
deleted file mode 100644
index 42526de..0000000
--- a/gas/testsuite/gas/riscv/march-fail-order-z-std.d
+++ /dev/null
@@ -1,3 +0,0 @@
-#as: -march=rv32i_zicsr2p0_mafd
-#source: empty.s
-#error_output: march-fail-order-zx-std.l
diff --git a/gas/testsuite/gas/riscv/march-fail-order-zx-std.l b/gas/testsuite/gas/riscv/march-fail-order-zx-std.l
deleted file mode 100644
index 4f6b98c..0000000
--- a/gas/testsuite/gas/riscv/march-fail-order-zx-std.l
+++ /dev/null
@@ -1,2 +0,0 @@
-.*Assembler messages:
-.*Error: .*unknown prefix class for the ISA extension `mafd'
diff --git a/gas/testsuite/gas/riscv/march-fail-unknown-std.l b/gas/testsuite/gas/riscv/march-fail-unknown-std.l
index 834a485..1de7a42 100644
--- a/gas/testsuite/gas/riscv/march-fail-unknown-std.l
+++ b/gas/testsuite/gas/riscv/march-fail-unknown-std.l
@@ -1,2 +1,2 @@
 .*Assembler messages:
-.*Error: .*unknown standard ISA extension `y'
+.*Error: .*unknown standard ISA extension or prefix class `y'
diff --git a/gas/testsuite/gas/riscv/march-ok-reorder.d b/gas/testsuite/gas/riscv/march-ok-reorder.d
new file mode 100644
index 0000000..030f8b1
--- /dev/null
+++ b/gas/testsuite/gas/riscv/march-ok-reorder.d
@@ -0,0 +1,7 @@
+#as: -misa-spec=20191213 -march=rv32i2azicsr_fc2p0dxfoo2p0_m1_xbar2p0_zba
+#source: empty.s
+#readelf: -A
+
+Attribute Section: riscv
+File Attributes
+  Tag_RISCV_arch: "rv32i2p0_m1p0_a2p1_f2p2_d2p2_c2p0_zicsr2p0_zifencei2p0_zmmul1p0_zba1p0_xbar2p0_xfoo2p0"