Work around the broken way CocoaPods/Xcode deals with header maps

Summary:
See https://github.com/facebook/react-native/issues/14326 for the bug
this fixes.  This is a pretty ugly hack to work around what I think is
a CP bug.  Since the C++ dependencies are only needed to build RN
itself, and not applications, don't the conflicting headers as source
files.  Instead, use preserve_paths to get them unpacked into the
source tree under Pods/<Pod>, and arrange for them to get used with
HEADER_SEARCH_PATHS.  This keeps them out of the project, so they
don't get included in the header map, and other (badly structured)
projects don't get confused.

Reviewed By: javache

Differential Revision: D5254716

fbshipit-source-id: cf33dcbcc71b5247843650c33ccf4fb08378e584

React.podspec

@@ -107,7 +107,7 @@ Pod::Spec.new do |s|
     ss.source_files         = "ReactCommon/cxxreact/*.{cpp,h}"
     ss.exclude_files        = "ReactCommon/cxxreact/{JSCTracing,SampleCxxModule}.*"
     ss.private_header_files = "ReactCommon/cxxreact/*.h"
-    ss.pod_target_xcconfig  = { "HEADER_SEARCH_PATHS" => "\"$(PODS_TARGET_SRCROOT)/ReactCommon\" \"$(PODS_ROOT)/boost\" \"$(PODS_ROOT)/DoubleConversion\"" }
+    ss.pod_target_xcconfig  = { "HEADER_SEARCH_PATHS" => "\"$(PODS_TARGET_SRCROOT)/ReactCommon\" \"$(PODS_ROOT)/boost\" \"$(PODS_ROOT)/DoubleConversion\" \"$(PODS_ROOT)/Folly\"" }
   end
 
   s.subspec "ART" do |ss|

third-party-podspecs/Folly.podspec

@@ -13,14 +13,15 @@ Pod::Spec.new do |spec|
   spec.dependency 'GLog'
   spec.compiler_flags = '-DFOLLY_NO_CONFIG -DFOLLY_MOBILE=1 -DFOLLY_USE_LIBCPP=1'
   spec.header_mappings_dir = 'folly'
-  spec.source_files = 'folly/*.h',
-                      'folly/Bits.cpp',
+  spec.source_files = 'folly/Bits.cpp',
                       'folly/Conv.cpp',
                       'folly/Demangle.cpp',
                       'folly/StringBase.cpp',
                       'folly/Unicode.cpp',
                       'folly/dynamic.cpp',
                       'folly/json.cpp'
+  # workaround for https://github.com/facebook/react-native/issues/14326
+  spec.preserve_paths = 'folly/*.h'
   spec.libraries           = "stdc++"
   spec.pod_target_xcconfig = { "USE_HEADERMAP" => "NO",
                                "CLANG_CXX_LANGUAGE_STANDARD" => "c++14",

third-party-podspecs/GLog.podspec

@@ -10,7 +10,7 @@ Pod::Spec.new do |spec|
   spec.source = { :git => 'https://github.com/google/glog.git',
                   :tag => "v#{spec.version}" }
   spec.module_name = 'glog'
-  spec.source_files = 'src/**/*.h',
+  spec.source_files = 'src/glog/*.h',
                       'src/demangle.cc',
                       'src/logging.cc',
                       'src/raw_logging.cc',
@@ -18,8 +18,10 @@ Pod::Spec.new do |spec|
                       'src/symbolize.cc',
                       'src/utilities.cc',
                       'src/vlog_is_on.cc'
+  # workaround for https://github.com/facebook/react-native/issues/14326
+  spec.preserve_paths = 'src/*.h',
+                        'src/base/*.h'
   spec.exclude_files       = "src/windows/**/*"
-  spec.public_header_files = "src/glog/*.h"
   spec.libraries           = "stdc++"
   spec.pod_target_xcconfig = { "USE_HEADERMAP" => "NO",
                                "HEADER_SEARCH_PATHS" => "$(PODS_TARGET_SRCROOT)/src" }