Testcase for out-of-memory

Follow test/fuzz/README.md to install latest clang and libFuzzer then:

```
export PATH="$HOME/third_party/llvm-build/Release+Asserts/bin:$PATH"
export LIB_FUZZER_PATH="$HOME/src/compiler-rt/lib/fuzzer/libFuzzer.a"
./script/configure
./script/build-fuzzers ruby
./script/reproduce ruby ./oom-1
```

which gives:

```
/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer: Running 1 inputs 1 time(s) each.
Running: ./oom-1
==4257== ERROR: libFuzzer: out-of-memory (used: 1051Mb; limit: 1024Mb)
   To change the out-of-memory limit use -rss_limit_mb=<N>

Live Heap Allocations: 1086637843 bytes in 13638 chunks; quarantined: 669298 bytes in 104 chunks; 7256 other chunks; total chunks: 20998; showing top 95% (at most 8 unique contexts)
1055741504 byte(s) (97%) in 13495 allocation(s)
    0 0x4c180a in calloc /b/build/slave/linux_upload_clang/build/src/third_party/llvm/compiler-rt/lib/asan/asan_malloc_linux.cc:97:3
    1 0xa952fe in ts_calloc (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa952fe)
    2 0xa9492e in ts_tree_array_copy (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa9492e)
    3 0xaf1479 in ts_stack_pop_count (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xaf1479)
    4 0xa5edbe in parser__reduce (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa5edbe)
    5 0xa901af in parser__do_all_potential_reductions (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa901af)
    6 0xa6dc3d in parser__handle_error (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa6dc3d)
    7 0xa4e217 in parser__advance (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa4e217)
    8 0xa457a0 in parser_parse (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa457a0)
    9 0xa1461c in ts_document_parse_with_options (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0xa1461c)
    10 0x4f135a in LLVMFuzzerTestOneInput (/home/philipturnbull/src/tree-sitter/out/ruby_fuzzer+0x4f135a)
    11 0xb42d72 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /home/philipturnbull/src/compiler-rt/lib/fuzzer/./FuzzerLoop.cpp:517:13
    12 0xb35f4a in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) /home/philipturnbull/src/compiler-rt/lib/fuzzer/./FuzzerDriver.cpp:280:3
    13 0xb3a708 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) /home/philipturnbull/src/compiler-rt/lib/fuzzer/./FuzzerDriver.cpp:703:9
    14 0xb35ca0 in main /home/philipturnbull/src/compiler-rt/lib/fuzzer/./FuzzerMain.cpp:20:10
    15 0x7f092214f82f in __libc_start_main /build/glibc-bfm8X4/glibc-2.23/csu/../csu/libc-start.c:291

SUMMARY: libFuzzer: out-of-memory
```

oom-1

@@ -0,0 +1 @@
+,l:!.�inu

oom-2

@@ -0,0 +1 @@
+&if�F:*.�ensures

oom-3

@@ -0,0 +1 @@
+D		case{A,**(u(.:def{
k**,E

oom-4

@@ -0,0 +1 @@
+��r�*+=**ca=*ce*~f�case�T�;;;;..rs(.:2{��D`'rseher

script/reproduce

@@ -10,6 +10,8 @@ fi
 lang="$1"
 testcase="$2"
 
-out="out"
-ASAN_OPTIONS="quarantine_size_mb=10:detect_leaks=1" UBSAN="print_stacktrace=1:halt_on_error=1" \
-  "${out}/${lang}_fuzzer" "$testcase" -timeout=1 -runs=100
+out=$(cd $(dirname $0)/../out && pwd)
+export ASAN_OPTIONS="quarantine_size_mb=10:detect_leaks=1:symbolize=1"
+export UBSAN_OPTIONS="print_stacktrace=1:halt_on_error=1:symbolize=1"
+
+"${out}/${lang}_fuzzer" "$testcase" -timeout=10 -runs=1 -rss_limit_mb=1024

test/fuzz/README.md

@@ -8,8 +8,8 @@ The main fuzzing logic is implemented by `libFuzzer` which is part of the LLVM p
 
 ```
 cd ~/src
-git clone https://github.com/llvm-mirror/llvm
-cd llvm/lib/Fuzzer
+git clone https://github.com/llvm-mirror/compiler-rt
+cd compiler-rt/lib/fuzzer
 ./build.sh
 ```