package/tesseract-ocr: needs gcc >= 8

Since Buildroot commit [1] tesseract-ocr fails to build with gcc 7,
with error:

    src/api/baseapi.cpp:67:10: fatal error: filesystem: No such file or directory
     #include <filesystem> // for std::filesystem
              ^~~~~~~~~~~~

In Buildroot, tesseract-ocr has a C++17 requirement captured as
gcc >= 7. Gcc 7 has only a partial and experimental C++17 support,
which was sufficient, prior [1].

The tesseract-ocr upstream commit [2] introduced a usage of
std::filesystem. This commit is included in version 5.5.0,
bumped in [1].

The C++17 with std::filesystem support was introduced in gcc 8.1.
See [3].

This commit fixes the issue by raising the gcc version requirement to
8.x.

Fixes: f32da8b9844ae5f1b9dc6b7a89d7d9bd9d194f55

[1] https://gitlab.com/buildroot.org/buildroot/-/commit/f32da8b9844ae5f1b9dc6b7a89d7d9bd9d194f55
[2] https://github.com/tesseract-ocr/tesseract/commit/4e42f9de541f21acb010886925afe42094a15dfe
[3] https://gcc.gnu.org/gcc-8/changes.html#libstdcxx

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
(cherry picked from commit 22ffdea9e65056a4e1c5307963962e05b5b6f0dc)

package/tesseract-ocr/Config.in

@@ -1,13 +1,13 @@
-comment "tesseract-ocr needs a toolchain w/ threads, C++, gcc >= 7, dynamic library, wchar"
+comment "tesseract-ocr needs a toolchain w/ threads, C++, gcc >= 8, dynamic library, wchar"
 	depends on BR2_USE_MMU
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_HAS_THREADS || \
-		!BR2_TOOLCHAIN_GCC_AT_LEAST_7 || BR2_STATIC_LIBS || !BR2_USE_WCHAR
+		!BR2_TOOLCHAIN_GCC_AT_LEAST_8 || BR2_STATIC_LIBS || !BR2_USE_WCHAR
 
 menuconfig BR2_PACKAGE_TESSERACT_OCR
 	bool "tesseract-ocr"
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_TOOLCHAIN_HAS_THREADS
-	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_7 # C++17
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_8 # C++17 filesystem
 	depends on BR2_USE_MMU # fork()
 	depends on !BR2_STATIC_LIBS
 	depends on BR2_USE_WCHAR