Revert "Revert "arch: Add support for loong64 CPU""

This reverts commit f9187c8b.

This reintroduces the loong64 CPU support that got reverted. The GNU
triplet and the multiarch tuples have gone back upstream to the previous
agreed names.

Closes: #1028654

data/cputable

@@ -26,6 +26,7 @@ arm		arm		arm.*			32	little
 arm64		aarch64		aarch64			64	little
 avr32		avr32		avr32			32	big
 hppa		hppa		hppa.*			32	big
+loong64		loongarch64	loongarch64		64	little
 i386		i686		(i[34567]86|pentium)	32	little
 ia64		ia64		ia64			64	little
 m32r		m32r		m32r			32	big

scripts/Dpkg/Shlibs/Objdump.pm

@@ -104,6 +104,7 @@ use constant {
     EM_XTENSA               => 94,
     EM_MICROBLAZE           => 189,
     EM_ARCV2                => 195,
+    EM_LOONGARCH            => 258,
     EM_AVR_OLD              => 0x1057,
     EM_OR1K_OLD             => 0x8472,
     EM_ALPHA                => 0x9026,
@@ -128,6 +129,11 @@ use constant {
 
     EF_IA64_ABI64           => 0x00000010,
 
+    EF_LOONGARCH_SOFT_FLOAT     => 0x00000001,
+    EF_LOONGARCH_SINGLE_FLOAT   => 0x00000002,
+    EF_LOONGARCH_DOUBLE_FLOAT   => 0x00000003,
+    EF_LOONGARCH_ABI_MASK       => 0x00000007,
+
     EF_MIPS_ABI2            => 0x00000020,
     EF_MIPS_32BIT           => 0x00000100,
     EF_MIPS_FP64            => 0x00000200,
@@ -161,6 +167,7 @@ my %elf_mach_map = (
 # behavior, and we do not drop dependencies.
 my %elf_flags_mask = (
     EM_IA64()               => EF_IA64_ABI64,
+    EM_LOONGARCH()          => EF_LOONGARCH_ABI_MASK,
     EM_MIPS()               => EF_MIPS_ABI_MASK | EF_MIPS_ABI2,
     EM_PPC64()              => EF_PPC64_ABI64,
 );

scripts/t/Dpkg_Arch.t

@@ -16,7 +16,7 @@
 use strict;
 use warnings;
 
-use Test::More tests => 18407;
+use Test::More tests => 18900;
 
 use_ok('Dpkg::Arch', qw(debarch_to_debtuple debarch_to_multiarch
                         debarch_eq debarch_is debarch_is_wildcard
@@ -28,7 +28,7 @@ use_ok('Dpkg::Arch', qw(debarch_to_debtuple debarch_to_multiarch
                         get_host_gnu_type
                         get_valid_arches));
 
-my $KNOWN_ARCHES_TOTAL = 554;
+my $KNOWN_ARCHES_TOTAL = 569;
 my @valid_arches = get_valid_arches();
 
 sub get_valid_wildcards