dev-cpp/gsl: Initial addition

Closes: https://github.com/gentoo/gentoo/pull/6135

dev-cpp/gsl/Manifest

@@ -0,0 +1 @@
+DIST gsl-0_pre20171105.tar.gz 55870 SHA256 5adc4b4ba53102099f63b898da161469a854d4fd47e90195421fbe8bd8b50352 SHA512 0db9cae9af710c45f66d1e2b73e2002f921876d400165d13dbe9ede7aa9335249458a9f97d4eda4cff0b3a5ceebb6ef84b631310921011fedee8776fcec89e6a WHIRLPOOL 98e26057646f6be4cc6632901b2b45c5e46218e9048cd64561f7f118ee0e8feadeca3ca66a0b73a36a431b666fe7946c6f864dbcf97296bae3945b2350dcf2e5

dev-cpp/gsl/gsl-0_pre20171105.ebuild

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+# Copyright 1999-2017 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=6
+
+inherit cmake-utils vcs-snapshot
+
+DESCRIPTION="Guideline Support Library implementation by Microsoft"
+HOMEPAGE="https://github.com/Microsoft/GSL"
+SRC_URI="https://github.com/Microsoft/${PN}/tarball/d10ebc6555b627c9d1196076a78467e7be505987 -> ${P}.tar.gz"
+
+LICENSE="MIT"
+SLOT="0"
+KEYWORDS="~amd64 ~x86"
+IUSE="test"
+
+# header only library
+RDEPEND=""
+DEPEND="test? ( >=dev-cpp/catch-1.11.0 )"
+
+src_configure() {
+	local mycmakeargs=( -DGSL_TEST=$(usex test) )
+	cmake-utils_src_configure
+}

dev-cpp/gsl/metadata.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
+<pkgmetadata>
+	<maintainer type="person">
+		<email>gentoo@taujhe.de</email>
+		<description>Jan Henke</description>
+	</maintainer>
+	<maintainer type="project">
+		<email>proxy-maint@gentoo.org</email>
+		<name>Proxy Maintainers</name>
+	</maintainer>
+	<longdescription>Microsoft's implmentation of the Guideline Support Library.</longdescription>
+	<upstream>
+		<remote-id type="github">Microsoft/GSL</remote-id>
+	</upstream>
+</pkgmetadata>