Ramp up CMake to v3 (#991)

Drive-by: drop premake5 support

CMakeLists.txt

@@ -1,8 +1,7 @@
-# Ubuntu 12.04 LTS has CMake 2.8.7, and is an important target since
-# several CI services, such as Travis and Drone, use it.  Solaris 11
-# has 2.8.6, and it's not difficult to support if you already have to
-# support 2.8.7.
-cmake_minimum_required(VERSION 2.8.6)
+# Available CMake versions:
+#  - Ubuntu 18.04 LTS (deprecated on GitHub Actions) : 3.10.4
+#  - Solaris 11.4 SRU 15                             : 3.15 
+cmake_minimum_required(VERSION 3.10.4)
 
 # Since this project's version is loaded from other files, this policy
 # will help suppress the warning generated by cmake.

premake5.lua

@@ -1,78 +0,0 @@
--- A solution contains projects, and defines the available configurations
-solution "brotli"
-configurations { "Release", "Debug" }
-platforms { "x64", "x86" }
-targetdir "bin"
-location "buildfiles"
-flags "RelativeLinks"
-includedirs { "c/include" }
-
-filter "configurations:Release"
-  optimize "Speed"
-  flags { "StaticRuntime" }
-
-filter "configurations:Debug"
-  flags { "Symbols" }
-
-filter { "platforms:x64" }
-   architecture "x86_64"
-
-filter { "platforms:x86" }
-   architecture "x86"
-
-configuration { "gmake" }
-  buildoptions { "-Wall -fno-omit-frame-pointer" }
-  location "buildfiles/gmake"
-
-configuration { "xcode4" }
-  location "buildfiles/xcode4"
-
-configuration "linux"
-  links "m"
-
-configuration { "macosx" }
-  defines { "OS_MACOSX" }
-
-project "brotlicommon"
-  kind "SharedLib"
-  language "C"
-  files { "c/common/**.h", "c/common/**.c" }
-
-project "brotlicommon_static"
-  kind "StaticLib"
-  targetname "brotlicommon"
-  language "C"
-  files { "c/common/**.h", "c/common/**.c" }
-
-project "brotlidec"
-  kind "SharedLib"
-  language "C"
-  files { "c/dec/**.h", "c/dec/**.c" }
-  links "brotlicommon"
-
-project "brotlidec_static"
-  kind "StaticLib"
-  targetname "brotlidec"
-  language "C"
-  files { "c/dec/**.h", "c/dec/**.c" }
-  links "brotlicommon_static"
-
-project "brotlienc"
-  kind "SharedLib"
-  language "C"
-  files { "c/enc/**.h", "c/enc/**.c" }
-  links "brotlicommon"
-
-project "brotlienc_static"
-  kind "StaticLib"
-  targetname "brotlienc"
-  language "C"
-  files { "c/enc/**.h", "c/enc/**.c" }
-  links "brotlicommon_static"
-
-project "brotli"
-  kind "ConsoleApp"
-  language "C"
-  linkoptions "-static"
-  files { "c/tools/brotli.c" }
-  links { "brotlicommon_static", "brotlidec_static", "brotlienc_static" }