fix compilation on Windows

[apwojcik]

The function flatten is missing MIGRAPHX_EXPORT, and that broke compilation on Windows.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.77%. Comparing base (e4013bb) to head (6915c5d).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2985   +/-   ##
========================================
  Coverage    91.77%   91.77%           
========================================
  Files          484      484           
  Lines        18711    18711           
========================================
  Hits         17172    17172           
  Misses        1539     1539           

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[migraphx-bot]

Test	Batch	Rate new 6915c5	Rate old e4013b	Diff	Compare
torchvision-resnet50	64	2,827.04	2,823.82	0.11%	✅
torchvision-resnet50_fp16	64	6,573.15	6,573.76	-0.01%	✅
torchvision-densenet121	32	2,099.77	2,099.78	-0.00%	✅
torchvision-densenet121_fp16	32	3,694.25	3,697.45	-0.09%	✅
torchvision-inceptionv3	32	1,605.85	1,606.34	-0.03%	✅
torchvision-inceptionv3_fp16	32	2,553.54	2,557.73	-0.16%	✅
cadene-inceptionv4	16	717.79	717.42	0.05%	✅
cadene-resnext64x4	16	680.48	680.58	-0.01%	✅
slim-mobilenet	64	5,914.04	5,900.96	0.22%	✅
slim-nasnetalarge	64	153.88	154.13	-0.16%	✅
slim-resnet50v2	64	2,587.04	2,589.06	-0.08%	✅
bert-mrpc-onnx	8	919.59	959.97	-4.21%	🔴
bert-mrpc-tf	1	394.96	437.51	-9.73%	🔴
pytorch-examples-wlang-gru	1	390.64	394.48	-0.97%	✅
pytorch-examples-wlang-lstm	1	374.92	368.26	1.81%	✅
torchvision-resnet50_1	1	603.70	603.31	0.06%	✅
cadene-dpn92_1	1	387.00	390.51	-0.90%	✅
cadene-resnext101_1	1	332.31	332.67	-0.11%	✅
onnx-taau-downsample	1	307.10	307.12	-0.01%	✅
dlrm-criteoterabyte	1	28.80	28.79	0.01%	✅
dlrm-criteoterabyte_fp16	1	48.35	48.37	-0.03%	✅
agentmodel	1	7,307.59	7,319.52	-0.16%	✅
unet_fp16	2	57.73	57.21	0.92%	✅
resnet50v1_fp16	1	885.95	891.91	-0.67%	✅
resnet50v1_int8	1	800.24	801.04	-0.10%	✅
bert_base_cased_fp16	64	1,053.26	1,053.68	-0.04%	✅
bert_large_uncased_fp16	32	301.62	301.67	-0.02%	✅
bert_large_fp16	1	158.81	158.77	0.02%	✅
distilgpt2_fp16	16	1,859.41	1,860.76	-0.07%	✅
yolov5s	1	477.09	469.23	1.68%	✅
tinyllama	1	32.98	32.98	-0.02%	✅
vicuna-fastchat	1	158.15	158.22	-0.04%	✅
whisper-tiny-encoder	1	348.85	348.40	0.13%	✅
whisper-tiny-decoder	1	395.25	395.77	-0.13%	✅

This build is not recommended to merge 🔴

[migraphx-bot]

     ✅ bert-mrpc-onnx: PASSED: MIGraphX meets tolerance

     ✅ bert-mrpc-tf: PASSED: MIGraphX meets tolerance

     ✅ pytorch-examples-wlang-gru: PASSED: MIGraphX meets tolerance

     ✅ pytorch-examples-wlang-lstm: PASSED: MIGraphX meets tolerance

     ✅ torchvision-resnet50_1: PASSED: MIGraphX meets tolerance

     ✅ cadene-dpn92_1: PASSED: MIGraphX meets tolerance

     ✅ cadene-resnext101_1: PASSED: MIGraphX meets tolerance

     ✅ dlrm-criteoterabyte: PASSED: MIGraphX meets tolerance

     ✅ agentmodel: PASSED: MIGraphX meets tolerance

     ✅ unet: PASSED: MIGraphX meets tolerance

     ✅ resnet50v1: PASSED: MIGraphX meets tolerance

     ✅ bert_base_cased_fp16: PASSED: MIGraphX meets tolerance

🔴bert_large_uncased_fp16: FAILED: MIGraphX is not within tolerance - check verbose output

     ✅ bert_large: PASSED: MIGraphX meets tolerance

     ✅ yolov5s: PASSED: MIGraphX meets tolerance

     ✅ tinyllama: PASSED: MIGraphX meets tolerance

     ✅ vicuna-fastchat: PASSED: MIGraphX meets tolerance

     ✅ whisper-tiny-encoder: PASSED: MIGraphX meets tolerance

     ✅ whisper-tiny-decoder: PASSED: MIGraphX meets tolerance

     ✅ distilgpt2_fp16: PASSED: MIGraphX meets tolerance