Bug 1847958 - Use -Oz for optimize option on GeckoView all channels. r=firefox-build-system-reviewers,glandium

Due to size limit of APK, we should use `-Oz` instead of `-O2` even if Nightly.
Actually, Nightly is `-O2` and Others (Beta and Release) are `-Oz`.

As long as I look perf data (bug 1831935 etc) after testing -O2, improvement is still
small (It seems to be small improvement of AndroidStartup only).

Also, this fix removes gcc support of GeckoView build since NDK removes gcc now.

Differential Revision: https://phabricator.services.mozilla.com/D185817

old-configure.in

@@ -369,31 +369,23 @@ case "$target" in
     ;;
 
 *-android*|*-linuxandroid*)
-    if test -z "$CLANG_CC"; then
-        MOZ_OPTIMIZE_FLAGS="-freorder-blocks -fno-reorder-functions -Os"
-    else
-        if test -n "$NIGHTLY_BUILD"; then
-            MOZ_OPTIMIZE_FLAGS="-O2"
-        else
-            # From https://github.com/android-ndk/ndk/issues/133#issuecomment-308549264
-            # -Oz is smaller than -Os on clang.
-            MOZ_OPTIMIZE_FLAGS="-Oz"
-            # Disable the outliner, which causes performance regressions, and is
-            # enabled on some platforms at -Oz.
-            if test -z "$MOZ_LTO"; then
-                DISABLE_OUTLINER="-mno-outline"
-                _SAVE_CFLAGS=$CFLAGS
-                CFLAGS="$CFLAGS $DISABLE_OUTLINER"
-                AC_TRY_COMPILE(,,[MOZ_OPTIMIZE_FLAGS="$MOZ_OPTIMIZE_FLAGS $DISABLE_OUTLINER"])
-                CFLAGS="$_SAVE_CFLAGS"
-            else
-                DISABLE_OUTLINER="-Wl,-plugin-opt=-enable-machine-outliner=never"
-                _SAVE_LDFLAGS=$LDFLAGS
-                LDFLAGS="$LDFLAGS $MOZ_LTO_LDFLAGS $DISABLE_OUTLINER"
-                AC_TRY_LINK(,,[MOZ_OPTIMIZE_LDFLAGS="$MOZ_OPTIMIZE_LDFLAGS $DISABLE_OUTLINER"])
-                LDFLAGS="$_SAVE_LDFLAGS" 
-            fi
-        fi
+    # From https://github.com/android-ndk/ndk/issues/133#issuecomment-308549264
+    # -Oz is smaller than -Os on clang.
+    MOZ_OPTIMIZE_FLAGS="-Oz"
+    # Disable the outliner, which causes performance regressions, and is
+    # enabled on some platforms at -Oz.
+    if test -z "$MOZ_LTO"; then
+        DISABLE_OUTLINER="-mno-outline"
+        _SAVE_CFLAGS=$CFLAGS
+        CFLAGS="$CFLAGS $DISABLE_OUTLINER"
+        AC_TRY_COMPILE(,,[MOZ_OPTIMIZE_FLAGS="$MOZ_OPTIMIZE_FLAGS $DISABLE_OUTLINER"])
+        CFLAGS="$_SAVE_CFLAGS"
+   else
+        DISABLE_OUTLINER="-Wl,-plugin-opt=-enable-machine-outliner=never"
+        _SAVE_LDFLAGS=$LDFLAGS
+        LDFLAGS="$LDFLAGS $MOZ_LTO_LDFLAGS $DISABLE_OUTLINER"
+        AC_TRY_LINK(,,[MOZ_OPTIMIZE_LDFLAGS="$MOZ_OPTIMIZE_LDFLAGS $DISABLE_OUTLINER"])
+        LDFLAGS="$_SAVE_LDFLAGS"
     fi
     ;;