deps: fix gypi sysroot settings on V8

On Node.js v8.x, gn will pass a sysroot parameter to clang to use a
downloaded sysroot files while running `make test-v8`. Recently,
chromium build tools switched to use Debian sid sysroot files instead of
Debian jessie. This patch updates our V8 GYP files to conform with those
changes.

Ref: #21433

PR-URL: #21494
Refs: #21433
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

deps/v8/gypfiles/standalone.gypi

@@ -93,16 +93,16 @@
           ['OS=="linux" and use_sysroot==1', {
             'conditions': [
               ['target_arch=="arm"', {
-                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_jessie_arm-sysroot',
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_sid_arm-sysroot',
               }],
               ['target_arch=="x64"', {
-                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_jessie_amd64-sysroot',
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_sid_amd64-sysroot',
               }],
               ['target_arch=="ia32"', {
-                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_jessie_i386-sysroot',
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_sid_i386-sysroot',
               }],
               ['target_arch=="mipsel"', {
-                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_jessie_mips-sysroot',
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_sid_mips-sysroot',
               }],
             ],
           }], # OS=="linux" and use_sysroot==1