SERVER-27682 Use variables files to configure toolchains

(cherry picked from commit 4052dc6)

Only the toolchain variables files for GCC and Clang were taken

(cherry picked from commit b664f75)

etc/scons/mongodbtoolchain_clang.vars

@@ -0,0 +1,22 @@
+# Configures the build to use the Clang toolchain in /opt/mongodbtoolchain/v2
+
+import os
+import SCons.Defaults
+
+# Get the default SCons path as a list
+default_path = SCons.Defaults.DefaultEnvironment()['ENV']['PATH'].split(os.pathsep)
+
+# Put the toolchain path first so we prefer all tools from there in subprocs.
+ENV = {
+    'PATH' : os.pathsep.join(['/opt/mongodbtoolchain/v2/bin'] + default_path)
+}
+
+# Set any Variables for Tools from the toolchain here. Technically, we
+# shouldn't need the full paths since SCons will find the toolchain
+# ones first, but we don't want to accidentally get the system version
+# if, say, the toolchain is missing. Also, it is clearer that we are
+# getting the right toolchain in build log output when the path is
+# printed for each compiler invocation.
+CC = '/opt/mongodbtoolchain/v2/bin/clang'
+CXX = '/opt/mongodbtoolchain/v2/bin/clang++'
+OBJCOPY = '/opt/mongodbtoolchain/v2/bin/objcopy'

etc/scons/mongodbtoolchain_gcc.vars

@@ -0,0 +1,22 @@
+# Configures the build to use the GCC toolchain in /opt/mongodbtoolchain/v2
+
+import os
+import SCons.Defaults
+
+# Get the default SCons path as a list
+default_path = SCons.Defaults.DefaultEnvironment()['ENV']['PATH'].split(os.pathsep)
+
+# Put the toolchain path first so we prefer all tools from there in subprocs
+ENV = {
+    'PATH' : os.pathsep.join(['/opt/mongodbtoolchain/v2/bin'] + default_path)
+}
+
+# Set any Variables for Tools from the toolchain here. Technically, we
+# shouldn't need the full paths since SCons will find the toolchain
+# ones first, but we don't want to accidentally get the system version
+# if, say, the toolchain is missing. Also, it is clearer that we are
+# getting the right toolchain in build log output when the path is
+# printed for each compiler invocation.
+CC = '/opt/mongodbtoolchain/v2/bin/gcc'
+CXX = '/opt/mongodbtoolchain/v2/bin/g++'
+OBJCOPY = '/opt/mongodbtoolchain/v2/bin/objcopy'