Add support for LoongArch

boostcpp.jam

@@ -636,7 +636,7 @@ rule address-model ( )
     return <conditional>@boostcpp.deduce-address-model ;
 }
 
-local deducable-architectures = arm mips power riscv s390x sparc x86 combined ;
+local deducable-architectures = arm loongarch mips power riscv s390x sparc x86 combined ;
 feature.feature deduced-architecture : $(deducable-architectures) : propagated optional composite hidden ;
 for a in $(deducable-architectures)
 {
@@ -647,9 +647,10 @@ rule deduce-architecture ( properties * )
 {
     local result ;
     local filtered = [ toolset-properties $(properties) ] ;
-    local names = arm mips power riscv s390x sparc x86 combined ;
+    local names = arm loongarch mips power riscv s390x sparc x86 combined ;
     local idx = [ configure.find-builds "default architecture" : $(filtered)
         : /boost/architecture//arm
+        : /boost/architecture//loongarch
         : /boost/architecture//mips
         : /boost/architecture//power
         : /boost/architecture//riscv