$ make spec
Using /usr/bin/llvm-config [version=3.9.1]
./bin/crystal build  -o .build/all_spec spec/all_spec.cr
Using compiled compiler at .build/crystal
fork: Cannot allocate memory
0x888c2a: *Process::fork_internal<Bool>:(Int32 | Nil) at /home/maarten/crystal_debug/crystal/src/process.cr 127:7
0x889a43: *Process#initialize<String, Tuple(String), Nil, Bool, Bool, Bool, Bool, Bool, Nil>:Nil at /home/maarten/crystal_debug/crystal/src/process.cr 100:11
0x889572: *Process::new<String, Tuple(String), Nil, Bool, Bool, Bool, Bool, Bool, Nil>:Process at /home/maarten/crystal_debug/crystal/src/process.cr 197:3
0x88947b: *Process::run:output<String, Tuple(String), Bool>:Process::Status at /home/maarten/crystal_debug/crystal/src/process.cr 145:14
0x8cfc40: *Crystal::Program#lib_flags:String at /home/maarten/crystal_debug/crystal/src/compiler/crystal/codegen/link.cr 96:32
0x1393b82: *Crystal::Compiler#codegen<Crystal::Program, Crystal::ASTNode+, Array(Crystal::Compiler::Source), String>:(Tuple(Array(Crystal::Compiler::CompilationUnit), Array(String)) | Nil) at /home/maarten/crystal_debug/crystal/src/compiler/crystal/compiler.cr 244:7
0x1396343: *Crystal::Compiler#compile<Array(Crystal::Compiler::Source), String>:Crystal::Compiler::Result at /home/maarten/crystal_debug/crystal/src/compiler/crystal/compiler.cr 138:16
0x14cebf9: *Crystal::Command::CompilerConfig#compile<String>:Crystal::Compiler::Result at /home/maarten/crystal_debug/crystal/src/compiler/crystal/command.cr 259:7
0x14ceba2: *Crystal::Command::CompilerConfig#compile:Crystal::Compiler::Result at /home/maarten/crystal_debug/crystal/src/compiler/crystal/command.cr 257:5
0x88d5e2: *Crystal::Command#build:Crystal::Compiler::Result at /home/maarten/crystal_debug/crystal/src/compiler/crystal/command.cr 175:5
0x88c9e8: *Crystal::Command#run:(Bool | Crystal::Compiler::Result | IO::FileDescriptor | Nil) at /home/maarten/crystal_debug/crystal/src/compiler/crystal/command.cr 72:9
0x88c6eb: *Crystal::Command::run<Array(String)>:(Bool | Crystal::Compiler::Result | IO::FileDescriptor | Nil) at /home/maarten/crystal_debug/crystal/src/compiler/crystal/command.cr 49:5
0x88c6a9: *Crystal::Command::run:(Bool | Crystal::Compiler::Result | IO::FileDescriptor | Nil) at /home/maarten/crystal_debug/crystal/src/compiler/crystal/command.cr 48:3
0x74ffcb: ??? at /home/maarten/crystal_debug/crystal/src/compiler/crystal.cr 8:1
0x75edf9: main at /home/maarten/.cache/crystal/macro61811040.cr 12:15
0x7fd311394511: __libc_start_main at ??
0x74f20a: _start at ??
0x0: ??? at ??