GCC toolchain: Add {SYSROOT} substitution with support for whitespaces

Any instance of {SYROOT} string in config's CFLAGS and LDFLAGS is replaced by sysroot path obtained from "gcc -print-sysroot"

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*.pyc

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**/__pycache__

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.vscode

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**/build/**

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*.class

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**/.svghmithumbs/**

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**/my_*.der

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**/my_*.pem

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tests/tools/Docker/requirements.txt