Include <alloca.h> also when __SWITCH__ is defined (#2595)
Include <alloca.h> also when __SWITCH__ is defined (#2595)

Fixes compilation with devkitPro for Nintendo Switch
bkaradzic/imgui,cmaughan/imgui,nProtect/imgui,aimotive/imgui-glfw,ggtucker/imgui,dougbinks/imgui,ggtucker/imgui,burningreggae/imgui,bkaradzic/imgui,cmaughan/imgui,nProtect/imgui,aimotive/imgui-glfw,bkaradzic/imgui,cmaughan/imgui,ocornut/imgui,Flix01/imgui,burningreggae/imgui,Flix01/imgui,ggtucker/imgui,cmaughan/imgui,Flix01/imgui,ocornut/imgui,ocornut/imgui,nProtect/imgui,dougbinks/imgui