Rename RTC_EXPORT to RTC_OBJC_EXPORT.

A new version of RTC_EXPORT will be introduced by [1] and it will be
used by WebRTC native code.

This CL renames the current RTC_EXPORT to RTC_OBJC_EXPORT in order
to avoid to mix them. It has been decided to avoid to unify them because
RTC_OBJC_EXPORT always marks symbols with default visibility, while
RTC_EXPORT will do it only when COMPONENT_BUILD is defined.

[1] - https://webrtc-review.googlesource.com/c/src/+/97960 is

Bug: webrtc:9419
Change-Id: I56a3fc6601c72d3ad6a58f9961a00e3761dfb5da
Reviewed-on: https://webrtc-review.googlesource.com/100521
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24754}
diff --git a/sdk/objc/components/video_codec/RTCCodecSpecificInfoH264.h b/sdk/objc/components/video_codec/RTCCodecSpecificInfoH264.h
index e9af571..ece9570 100644
--- a/sdk/objc/components/video_codec/RTCCodecSpecificInfoH264.h
+++ b/sdk/objc/components/video_codec/RTCCodecSpecificInfoH264.h
@@ -19,7 +19,7 @@
   RTCH264PacketizationModeSingleNalUnit        // Mode 0 - only single NALU allowed
 };
 
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCCodecSpecificInfoH264 : NSObject <RTCCodecSpecificInfo>
 
 @property(nonatomic, assign) RTCH264PacketizationMode packetizationMode;
diff --git a/sdk/objc/components/video_codec/RTCDefaultVideoDecoderFactory.h b/sdk/objc/components/video_codec/RTCDefaultVideoDecoderFactory.h
index 1ad9c43..7ca9463 100644
--- a/sdk/objc/components/video_codec/RTCDefaultVideoDecoderFactory.h
+++ b/sdk/objc/components/video_codec/RTCDefaultVideoDecoderFactory.h
@@ -18,7 +18,7 @@
 /** This decoder factory include support for all codecs bundled with WebRTC. If using custom
  *  codecs, create custom implementations of RTCVideoEncoderFactory and RTCVideoDecoderFactory.
  */
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCDefaultVideoDecoderFactory : NSObject <RTCVideoDecoderFactory>
 @end
 
diff --git a/sdk/objc/components/video_codec/RTCDefaultVideoEncoderFactory.h b/sdk/objc/components/video_codec/RTCDefaultVideoEncoderFactory.h
index b0e0af6..c45e543 100644
--- a/sdk/objc/components/video_codec/RTCDefaultVideoEncoderFactory.h
+++ b/sdk/objc/components/video_codec/RTCDefaultVideoEncoderFactory.h
@@ -18,7 +18,7 @@
 /** This encoder factory include support for all codecs bundled with WebRTC. If using custom
  *  codecs, create custom implementations of RTCVideoEncoderFactory and RTCVideoDecoderFactory.
  */
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCDefaultVideoEncoderFactory : NSObject <RTCVideoEncoderFactory>
 
 @property(nonatomic, retain) RTCVideoCodecInfo *preferredCodec;
diff --git a/sdk/objc/components/video_codec/RTCH264ProfileLevelId.h b/sdk/objc/components/video_codec/RTCH264ProfileLevelId.h
index 7b4e788..56b3532 100644
--- a/sdk/objc/components/video_codec/RTCH264ProfileLevelId.h
+++ b/sdk/objc/components/video_codec/RTCH264ProfileLevelId.h
@@ -12,11 +12,11 @@
 
 #import "RTCMacros.h"
 
-RTC_EXPORT extern NSString *const kRTCVideoCodecH264Name;
-RTC_EXPORT extern NSString *const kRTCLevel31ConstrainedHigh;
-RTC_EXPORT extern NSString *const kRTCLevel31ConstrainedBaseline;
-RTC_EXPORT extern NSString *const kRTCMaxSupportedH264ProfileLevelConstrainedHigh;
-RTC_EXPORT extern NSString *const kRTCMaxSupportedH264ProfileLevelConstrainedBaseline;
+RTC_OBJC_EXPORT extern NSString *const kRTCVideoCodecH264Name;
+RTC_OBJC_EXPORT extern NSString *const kRTCLevel31ConstrainedHigh;
+RTC_OBJC_EXPORT extern NSString *const kRTCLevel31ConstrainedBaseline;
+RTC_OBJC_EXPORT extern NSString *const kRTCMaxSupportedH264ProfileLevelConstrainedHigh;
+RTC_OBJC_EXPORT extern NSString *const kRTCMaxSupportedH264ProfileLevelConstrainedBaseline;
 
 /** H264 Profiles and levels. */
 typedef NS_ENUM(NSUInteger, RTCH264Profile) {
@@ -47,7 +47,7 @@
   RTCH264Level5_2 = 52
 };
 
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCH264ProfileLevelId : NSObject
 
 @property(nonatomic, readonly) RTCH264Profile profile;
diff --git a/sdk/objc/components/video_codec/RTCVideoDecoderFactoryH264.h b/sdk/objc/components/video_codec/RTCVideoDecoderFactoryH264.h
index 850ba7e..4fcff1d 100644
--- a/sdk/objc/components/video_codec/RTCVideoDecoderFactoryH264.h
+++ b/sdk/objc/components/video_codec/RTCVideoDecoderFactoryH264.h
@@ -13,6 +13,6 @@
 #import "RTCMacros.h"
 #import "RTCVideoDecoderFactory.h"
 
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCVideoDecoderFactoryH264 : NSObject <RTCVideoDecoderFactory>
 @end
diff --git a/sdk/objc/components/video_codec/RTCVideoDecoderH264.h b/sdk/objc/components/video_codec/RTCVideoDecoderH264.h
index 227200f..b860276 100644
--- a/sdk/objc/components/video_codec/RTCVideoDecoderH264.h
+++ b/sdk/objc/components/video_codec/RTCVideoDecoderH264.h
@@ -13,6 +13,6 @@
 #import "RTCMacros.h"
 #import "RTCVideoDecoder.h"
 
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCVideoDecoderH264 : NSObject <RTCVideoDecoder>
 @end
diff --git a/sdk/objc/components/video_codec/RTCVideoEncoderFactoryH264.h b/sdk/objc/components/video_codec/RTCVideoEncoderFactoryH264.h
index d185656..c64405e 100644
--- a/sdk/objc/components/video_codec/RTCVideoEncoderFactoryH264.h
+++ b/sdk/objc/components/video_codec/RTCVideoEncoderFactoryH264.h
@@ -13,6 +13,6 @@
 #import "RTCMacros.h"
 #import "RTCVideoEncoderFactory.h"
 
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCVideoEncoderFactoryH264 : NSObject <RTCVideoEncoderFactory>
 @end
diff --git a/sdk/objc/components/video_codec/RTCVideoEncoderH264.h b/sdk/objc/components/video_codec/RTCVideoEncoderH264.h
index d57713e..a9c0558 100644
--- a/sdk/objc/components/video_codec/RTCVideoEncoderH264.h
+++ b/sdk/objc/components/video_codec/RTCVideoEncoderH264.h
@@ -14,7 +14,7 @@
 #import "RTCVideoCodecInfo.h"
 #import "RTCVideoEncoder.h"
 
-RTC_EXPORT
+RTC_OBJC_EXPORT
 @interface RTCVideoEncoderH264 : NSObject <RTCVideoEncoder>
 
 - (instancetype)initWithCodecInfo:(RTCVideoCodecInfo *)codecInfo;