RISC-V: Enable elf attributes when default configure option isn't set.

Since gcc commit, 3c70b3ca1ef58f302bf8c16d9e7c7bb8626408bf, we now enable
elf attributes for all riscv targets by default in gcc.  Therefore, I
think binutils should have the same behavior, in case users are writing
assembly files.  If --enable-default-riscv-attribute isn't set, then we
enable the elf attributes for all riscv targets by default.

ChangLog:

binutils/

	* testsuite/binutils-all/readelf.s: Add comments for riscv.
	* testsuite/binutils-all/readelf.s-64: Likewise.
	* testsuite/binutils-all/readelf.s-64-unused: Likewise.
	* testsuite/binutils-all/readelf.ss: Likewise.
	* testsuite/binutils-all/readelf.ss-64: Likewise.
	* testsuite/binutils-all/readelf.ss-64-unused: Likewise.

gas/

	* configure.ac: If --enable-default-riscv-attribute isn't set,
	then we enable the elf attributes for all riscv targets by
	default.
	* configure: Regenerated.

binutils/testsuite/binutils-all/readelf.s

@@ -11,9 +11,10 @@ Section Headers:
 #...
  +\[ .\] .* +PROGBITS +00000000 0000(3c|40|44|48|50) 0000(04|10) 00 +WA +0 +0 +(.|..)
  +\[ .\] .* +NOBITS +00000000 0000(40|44|48|4c|60) 000000 00 +WA +0 +0 +(.|..)
-# ARM targets put .ARM.attributes here
+# ARM targets put .ARM.attributes here.
 # MIPS targets put .reginfo, .mdebug, .MIPS.abiflags and .gnu.attributes here.
 # v850 targets put .call_table_data and .call_table_text here.
+# riscv targets put .riscv.attributes here.
 #...
  +\[..\] .symtab +SYMTAB +00000000 0+.* 0+.* 10 +.. +.+ +4
  +\[..\] .strtab +STRTAB +00000000 0+.* 0+.* 00 .* +0 +0 +1

binutils/testsuite/binutils-all/readelf.s-64

@@ -14,10 +14,12 @@ Section Headers:
  +\[ 4\] .bss +NOBITS +0000000000000000 +000000(4c|50|54|58|68)
  +0000000000000000 +0000000000000000 +WA +0 +0 +.*
 # x86 targets may put .note.gnu.property here.
+# riscv targets put .riscv.attributes here.
 #...
  +\[ .\] .symtab +SYMTAB +0000000000000000 +0+.*
 # aarch64-elf targets have one more data symbol.
 # x86 targets may have .note.gnu.property.
+# riscv targets have .riscv.attributes.
  +0+.* +0000000000000018 +(6|7) +(3|4) +8
  +\[ .\] .strtab +STRTAB +0000000000000000 +0+.*
  +0+.* +0000000000000000 .* +0 +0 +1

binutils/testsuite/binutils-all/readelf.s-64-unused

@@ -14,10 +14,12 @@ Section Headers:
  +\[ 4\] .bss +NOBITS +0000000000000000 +000000(4c|50|54|58)
  +0000000000000000 +0000000000000000 +WA +0 +0 +.*
 # x86 targets may put .note.gnu.property here.
+# riscv targets put .riscv.attributes here.
 #...
  +\[ .\] .symtab +SYMTAB +0000000000000000 +0+.*
 # aarch64-elf targets have one more data symbol.
 # x86 targets may have .note.gnu.property.
+# riscv targets have .riscv.attributes.
  +0+.* +0000000000000018 +(6|7) +(6|7) +8
  +\[ .\] .strtab +STRTAB +0000000000000000 +0+.*
  +0+.* +0000000000000000 .* +0 +0 +1

binutils/testsuite/binutils-all/readelf.ss

@@ -9,6 +9,7 @@ Symbol table '.symtab' contains .* entries:
  +.: 00000000 +0 +NOTYPE +LOCAL +DEFAULT +[34] static_data_symbol
 # v850 targets include extra SECTION symbols here for the .call_table_data
 # and .call_table_text sections.
+# riscv targets add .riscv.attribute symbol here...
 #...
  +[0-9]+: 00000000 +0 +NOTYPE +GLOBAL +DEFAULT +1 text_symbol
  +[0-9]+: 00000000 +0 +NOTYPE +GLOBAL +DEFAULT +UND external_symbol

binutils/testsuite/binutils-all/readelf.ss-64

@@ -7,6 +7,7 @@ Symbol table '.symtab' contains .* entries:
 #...
  +.: 0000000000000000 +0 +NOTYPE +LOCAL +DEFAULT +3 static_data_symbol
 # ... or here ...
+# riscv targets add .riscv.attribute symbol here...
 #...
 .* +.: 0000000000000000 +0 +NOTYPE +GLOBAL +DEFAULT +1 text_symbol
  +.: 0000000000000000 +0 +NOTYPE +GLOBAL +DEFAULT +UND external_symbol

binutils/testsuite/binutils-all/readelf.ss-64-unused

@@ -10,6 +10,7 @@ Symbol table '.symtab' contains .* entries:
 #...
  +.: 0000000000000000 +0 +NOTYPE +LOCAL +DEFAULT +3 static_data_symbol
 # ... or here ...
+# riscv targets add .riscv.attribute symbol here...
 #...
 .* +.: 0000000000000000 +0 +NOTYPE +GLOBAL +DEFAULT +1 text_symbol
  +.: 0000000000000000 +0 +NOTYPE +GLOBAL +DEFAULT +UND external_symbol