ICU-20527 Fix a few issues in the top-level .gitignore file
diff --git a/.gitignore b/.gitignore
index f64b51f..df00707 100644
--- a/.gitignore
+++ b/.gitignore
@@ -49,7 +49,6 @@
icu4c/source/common/libicu*.*
icu4c/source/common/release
icu4c/source/common/svchook.mk
-icu4c/source/common/unicode/platform.h
icu4c/source/common/x64
icu4c/source/common/x86
icu4c/source/config.cache
@@ -218,7 +217,6 @@
icu4c/source/samples/coll/x86
icu4c/source/samples/csdet/*.vcxproj.user
icu4c/source/samples/csdet/Debug
-icu4c/source/samples/csdet/Makefile
icu4c/source/samples/csdet/csdet
icu4c/source/samples/csdet/csdet.exe
icu4c/source/samples/csdet/csdet.out
@@ -836,6 +834,7 @@
icu4c/source/tools/icuinfo/icuinfo
icu4c/source/tools/icuinfo/icuinfo.exe
icu4c/source/tools/icuinfo/icuplugins*.txt
+!icu4c/source/tools/icuinfo/icuplugins_windows_sample.txt
icu4c/source/tools/icuinfo/x64
icu4c/source/tools/icuinfo/x86
icu4c/source/tools/icupkg/*.8