Support building BoringSSL with NSS certificates.

build/linux/system.gyp

Index: build/linux/system.gyp
diff --git a/build/linux/system.gyp b/build/linux/system.gyp
index 9079011122c4f8948cb4db49e790976a52b7649f..36f7bd1b650922276f47da5a4e941541fe7f176c 100644
--- a/build/linux/system.gyp
+++ b/build/linux/system.gyp
@@ -1155,8 +1155,7 @@
               'dependencies': [
                 '../../third_party/boringssl/boringssl.gyp:boringssl',
               ],
-            }],
-            ['use_openssl==0', {
+            }, {
               'dependencies': [
                 '../../net/third_party/nss/ssl.gyp:libssl',
               ],
@@ -1166,6 +1165,10 @@
                   # before other includes, as we are shadowing system headers.
                   '<(DEPTH)/net/third_party/nss/ssl',
                 ],
+              },
+            }],
+            ['use_openssl==0 or use_nss==1', {

[Ryan Sleevi, 2015/02/23 20:37:40]

I am _deeply_ confused by these GYP variables, between system.gyp and
common.gypi

Could you document more _in the file_ what they mean and how they're set?

+              'direct_dependent_settings': {
                 'cflags': [
                   '<!@(<(pkg-config) --cflags nss)',
                 ],
@@ -1179,7 +1182,7 @@
                 ],
               },
             }],
-            ['use_openssl==0 and clang==1', {
+            ['(use_openssl==0 or use_nss==1) and clang==1', {
               'direct_dependent_settings': {
                 'cflags': [
                   # There is a broken header guard in /usr/include/nss/secmod.h: