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* add three external/google-fonts projects:
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* Add external/vixl
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* Update manifest for libivxl
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* Update manifest for libivxl
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* pin prebuilts/misc at older revision to avoid breakage
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* Add prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.11-4.[68]
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* Add vixl and prebuilt/clang to the dependencies of master-art-host.
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* Add external/ltrace to default.xml
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* remove external/libnl-headers from the manifest
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* DO NOT MERGE: Revert "remove external/libnl-headers from the manifest"
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* Add GCC 4.9 for aarch64.
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* Adds external/libcxx and external/libcxxabi to manifest